Given that not much widely used software uses ONC RPC still (at least I can't really think of anything that I'd call "widely used" save NFS off the top of my head) that's not surprising. That's not to say nobody uses it for some internal application, but things like several security holes in rpc.portmapper and what not put an end to widespread use on the Internet as a whole, IMSMR.

If there's a wrapper library available for the protocol you need you probably can use that via Inline::C; that's also probably going to be your best starting point to reimplement an ONC RPC module yourself (which I'm betting is what you're going to wind up doing, unfortunately). You should also look and see if there isn't an interface available in a more "up to date" RPC protocol such as SOAP, XML-RPC, or CORBA.

Update: Just thought of what'd be a tremendous kludge, but you might look through the source of old Linux distributions to see if you couldn't find an implementation of the ONC RPC libraries that's source compatible with what's on CPAN and then see if you can get those to compile instead of using what ships with your OS. But again, that'd be a tremendous kludge and possibly more effort than just rewriting your own perlrpcgen from scratch.