What type of board? Given that you mention KBC, I assume you're looking for Cherry compatible caps?
If that is the case, your best bet would be to get an older Cherry G81 with the correct layout. Possibly they would even be double shots, possibly lasered. I'm not aware of any dye sublimation keycaps from Cherry, but that doesn't mean there aren't any. I recommend the G81 over the G81 simply because they tend to be less expensive, which is, I assume, preferably in a keyboard you're going to strip the caps from. The older ones have the vintage two tone look you describe.
If it's ALPS, a Dell would be a good donor. For Topre, at least the main block, you can snag the HHKB white set from Elite Keyboards. For Buckling spring, there's Unicomp.
Also, maybe you should move this thread to the keycap subforum.