If you're looking to get a fully compatible, full set of keycaps, WASD (
www.wasdkeyboards.com) sells nice ABS keycaps in OEM profile. You can get them blank, laser etched, or engraved. Multiple colors are available, and you can design your own layout on their website. The spacebar fits a QFR just fine.
If you want double shot ABS instead, Signature Plastics sells standard sets on their marketplace page (
www.keycapsdirect.com). You can get them in either black with white print, or white with black print. Full sets cost the same, $60, as the WASD full sets. These area also fully compatible with your QFR.