The former Regina REXX developers have abandoned it and switched to supporting ooREXX. (Which does have an x64 version.)
Here is an email thread between myself and Mark Hessling, the Regina rexx maintainer --
No Regina is still very much in business. Some new capabilities are
being added (ability to start a new thread of execution from within your
The other reason that Regina is not going away is that with the 4.0
release of ooRexx, the SAA API has been broken (and the developers are
not prepared to fix it). This means that all of my Rexx related
products; THE, Rexx/SQL, etc cannot be built with ooRexx 4.0.