Sadly there are no custom keyboards with Topre at the moment (if I am wrong someone PLEASE correct me). Most custom boards you will find such as the Ergodox are made for Cherry MX switches - there may be a few that also support alps.
The problem is Topre switches revolve around carefully placed conductive springs with rubber domes that must be held in place. Unfortunately these are not self contained units and must be kept together in some other way. For instance the keys of the hhkb are literally held in place by the plastic case.
Show Image
(http://i.imgur.com/dgXCTCt.jpg)
WRONG
that is not why you can''t have custom topre
The main reason is the PCB
The capacitive nature of topre was only made after lots of testing to get the PCB sensors calibrated the correct way. DIYing a topre would take way to long and way to expensive for just one not mass produced keyboard
Making a plate for topre is mindless in comparison