IRWIN suggests the use of pre-formatted tapes for their tape drives, as
you often can't successfully format a tape and need  bulk-erase it before
you can format it again. Anyway, I have some new, preformatted tapes for
IRWIN 250 tape drives. 
IRWIN accuTRAK series 120-250MB, $16/ea. New never used.
3M DC2120, RHOMAT Format.  $16/ea. Wraped.

Email if interested.

Feng