The good news is that EK's HHKB set will work on the RealForce -- I'm using the red Control key (to replace Caps Lock) and the blue Esc key on mine (see photo).
The bad news is that it's pretty slim pickings in the Topre keycaps market. You can get the full sets that widebasket sells on eBay, and the limited options that EK has, but it gets tough after that. What I'd love to find, but haven't yet, is a Caps Lock key to replace the left Alt key (even though I know they exist because some RF boards have been sold with switchable Ctrl/Caps keycaps). I don't know where to find the blanks you're looking for, although if you spring for one of the full HHKB blank sets that EK sells, you might get most of what you want. They might not be perfect and might not give you the look you want --- I know EK says they're only for HHKB -- but I'd guess they'll work OK.
