Leopold is the manufacturer for all Topre keycaps. Realforce is a subsidiary of Leopold. IIRC Realforce keyboards even have Leopold on the label (or used to. I think mine does, I don't have it in front of me.)
However, I think they've improved the molds for their keycaps in recent years, which may or may not have something to do with the lack of custom keycaps on the market for topre.
Just my $0.02. I love my 45g realforce, but it's modded from a 55g. If you can find one, I definitely think it's worth going for. 55g seems to be a big favorite, though.