Most fabricators would buy HR flats 3/4 x 10, and cut off the 10-1/2" pieces as needed.
Steel service centers are happy to supply cut rectangles to exact dimensions, but charge a little extra for the cross-cuts and for handling the 'small' pieces.
Either way, just fax a RFQ describing what you want to all the service centers you can find, and pick from the quotes. Not rocket science.
Mike Halloran
Pembroke Pines, FL, USA