The most common PVM platform is a Unix machine, and PVM currently runs on more than 30 different ones. Chances are, yours is included. Porting it to other ones is generally a simple matter. A complete list of predefined architectures can be found in the PVM source in file doc/arches.
Special ports of PVM for some message-passing processors are included with the Netlib distribution. These include the Intel iPSC/860, iPSC/2 and Paragon and TMC CM-5. Shared memory ports are also included that use System-5 shared memory for communication and run on Sun, SGI, DEC, Kendall Square, Sequent and IBM machines.
Ports exist aside from the Netlib distribution for the Cray T-3D (a CRI product), Parsytech ( I don't have a reference for this one) and other machines. Ports have also been done to VMS (by Dan Clark, email@example.com) and OS/2 (by Jan Ftacnik, firstname.lastname@example.org).