I know I have used the odd Pro Pad Fin for a spacer on a rear brake on show builds and I have seen others do the same.
Also, some collectors mix and match the colours of the pads and fins to detail theyre builds.
I guess there are alot more fins around than pads, hence there always being fins available - even if it is at a silly price.
I havent seen red pro pads for sale for a while. Dont think I have any but will check later.