Widebasket's store, EK (if they still carry the HHKB replacement sets), or the classifieds.
Topre keycaps are extremely hard to come by, as they are no longer produced.
It sounds like you're describing the Ducky 2013 edition Realforce almost perfectly:Show Image(http://i307.photobucket.com/albums/nn316/peternmelly/20131129_092756.jpg)