I purchased some Bakers and Chefs clear plastic squeeze bottles, which do not come with caps; however, there is a ridge about 1/3" down on the bottle, suggesting that they're intended to work with a cap.  Some of the reviewers on Amazon mentioned using foil, as well as some plastic cap they found in hardware store. I'm hoping to find something that fits well and ideally can be ordered online.    Anyone have any suggestions? 
I've been searching for a while.  I use my squeeze bottles for various things, and the tip caps are helpful.  It keeps royal icing from drying out, and prevents leaks when shaking up a bottle of vinaigrette.  Here's what I found: http://www.usplastic.com/catalog/item.aspx?itemid=91498&catid=536  http://www.dharmatrading.com/tools/squeeze-bottles-yorker-spouts-and-caps.html 