Yes, you can buy blank hex pieces.
Print&Play
Productions offers cardboard hex tiles in several different sizes through Boards & Bits .
Chipboard Shapes - Hex 1.19"
[35 pcs]
$2.00Chipboard Shapes - Hex 1.5" [20 pcs]
$2.00Chipboard Shapes - Hex 2.2" [11 pcs]
$2.00Chipboard Shapes - Hex 2.6" [22 pcs]
$3.00Chipboard Shapes - Hex 3.9" [8 pcs] $3.00
You could also get wooden hexes from WoodNShop for $0.15-$0.42 each, or at a discount by the 100s.
I am unsure if these would fit your purposes for tile laying, as I have heard complaints that the tile dimensions are not uniform enough for such a purpose.
C/O HEXAGON 1/8
X 1 $0.15
C/O HEXAGON
1/8
X 2 $0.20
C/O HEXAGON
1/8
X 1 $0.32
C/O HEXAGON
1/8
X 1 $0.42
C/O HEXAGON 1/4
X 2 $0.20
There is also plastic tiles , if you are so inclined.
With a little bit of work to remove the mesh backing, you could use actual hexagonal tiles from your local hardware store .
I don't know of any board game manufacturer that creates hex tiles with custom graphics.
Board game maufacturers are capable of creating protype board games, but my guess is the cost is prohibitive.
If you want to cut your own uniform hex tiles, you are going to need a die cutter ($600), and a custom die .
You probably don't even need hex tiles for testing purposes.
If the hex tiles need not be rotated, then square tiles can be offset every other row for the same effect as a hex tile.
If orientation is important, wooden tiles/disks can be substituted for hex tiles.
boardgames.stackexchange.com/users/1873/user1873
Quilters and schools often use die-cutters to make shaped pieces.
Hexagons are one of the standard die types, and are available in a variety of sizes.
Many cut multiples at once, tho the standard sized template is a 5x8" block with 1 large, or 2, 4, or 6 hexagons of smaller sizes (3", 2", 1" face to face) Search for Hexagon die cut to find more variety than is worth listing here.
Craft stores and school supply stores often also have them.
To use them, however, you'll want a die-cutting press - itself a hundred dollar item.
boardgames.stackexchange.com/users/1047/aramis
at the Wikipedia entry for hexagons( http://en.wikipedia.org/wiki/Hexagon )
there is a really neat gif on how to draw a normal hexagon with a compass and a straight edge.
Otherwise I've used TheGameCrafter.com in the past.
They have a Hex playing cards .
although that's probably larger then catan.
(3.75in X 3.25in).
and you can even get blanks there (if they have them in stock.)
boardgames.stackexchange.com/users/None/
Another source worth checking out, specifically for the games market, is Blue Panther LLC: they seem to make pieces specifically for gaming and can do custom cuts or engravings when you're ready to take that step.
Have a look at http://www.bluepantherllc.com/ for the details.
I've done my own prototyping with wood pattern blocks, an educational tool you can find at a lot of school-supply stores; I was lucky enough to find a bag of nothing but hexes, but the shop I got it from has no idea what the model/part number on that bag was (if any) and I can't seem to find specifically hex-shaped pieces online, just a set of hexes, triangles, squares, etc.
boardgames.stackexchange.com/users/2007/Steven Stadnicki
Disclaimer:
I own this business.
Prawn Designs , based in California, sells custom bits and bases , including hexes.
boardgames.stackexchange.com/users/7288/Bob Schrempp
FYI:
It isn't going to look as pretty as real hex tiles
but if you are just prototyping a game then you can functionally simulate Hexes tiles with Square tiles since six squares can fit around each square if you stagger rows.
Drawing dots one quarter and three quarters down each edge and connect the nearest dots with lines makes the hex nature of squares more apparent.
Real life example of someone using just square tiles to create a hex board: https://www.boardgamegeek.com/image/786116/beehive
boardgames.stackexchange.com/users/18119/Trevor
Fellow board game player wants to test his game prototype, which uses a number of hex pieces (prefreably smaller than Catan or Eclipse ones). Is there a place to buy some blank ones? We could then use adhesive paper labels printed on inkjet printer. Or maybe there is a place to send full-hex graphic design and receive cutted pieces? Alternatively, do you have working DIY methods for cutting uniform hexes?
Where to buy or how to cut blank hexes for own game prototype?
boardgames.stackexchange.com
<custom-game-pieces>
boardgames.stackexchange.com/questions/7974
boardgames.stackexchange.com/users/3106/tomash
You can buy wooden or cardboard hex tiles. You can also custom game pieces.  If you want to cut your own uniform hex tiles you will need a  die cutter and a  custom die .  Or wooden tiles or discs can be substituted for hex tiles. If you draw dots one quarter and three quarters down each edge and connect the dots with lines, this gives a hex appearance.  Blue Panther LLC make pieces specifically for gaming and can do custom cuts or engraving and Prawn Designs in California, sells  custom bits and bases , including hexes.
Boards & Bits have cardboard hex tiles in several different sizes by Production and WoodNShop also have wooden hexes at $0.15-$0.42 each, or at a discount price by the 100s.  If you want to cut your own uniform hex tiles you will need a  die cutter and a  custom die .  Or wooden tiles or discs can be substituted for hex tiles. If you draw dots one quarter and three quarters down each edge and connect the dots with lines, this gives a hex appearance.   Blue Panther LLC make pieces specifically for gaming and can do custom cuts or engraving and Prawn Designs in California, sells  custom bits and bases , including hexes.