dont know of any firms that are FX only arcades, but most firms will let you trade FX especially if you have a track record cant imagine it being a problem, especially the futures maket its traded on CME and most guys have a CME log-in anyway.
As charliechan says FX isnt as liquid as STIRS but that of course is FX futures, some places will let you trade the cash market. If you get a partial fill in that as a self funded trader congratulations!