I'm not sure where in the US you can get blank or pre-printed sheets (being from Australia) but www.bsk.co.uk have a supply of blank ones and if you email scanthecat at ScanTheCat@aol.com they may be able to point you in the right direction.
There is a supplier here in Australia but they don't have a website and don't take credit card payments (I know).
I think somebody could make a bit of money if they could come up with a supplier for the brother 910 electroknit machine. I just acquired one of these machines and it looks like it was well taken care of. I purchased a cord from ebay the green light comes on so I'm pretty sure it will work if I could just find a 60 stitch mylar sheet. I have looked all over ebay and pretty much found nothing. If anyone would care to share any bits of knowledge about the elusive 60 stitch mylar sheets for the brother kH-910 electroknit machine I would greatly appreciate it. Thanks ragmom123