Well 87 Black Blank PBT keycaps aren't that hard to find if you try, though I don't know about profile/thickness.
The only thing I am slightly worried about for the group buy is colour matching a Shine 3, since the colour is referenced from Topre black on blacks.
I have no idea what a Realforce keyboard looks like in real life and photos seem to vary between grey and black, so I'm really not sure.