A recent post to the wheel-builders mailing list pointed out some links to places providing free PowerPC hosting for open source projects, if they agree to a submitted request:
The debian project has some powerpc machines (and we still build numpy on those boxes when i upload a new revision to our archives) and they also have hosts dedicated to let debian developers login and debug issues with their packages on that architecture. I can sponsor access to those machines for some of you, but it is not a place where you can host a CI instance.
Just keep it in mind more broadly than powerpc, f.e. these are all the archs where numpy was built after the last upload https://buildd.debian.org/status/package.php?p=python-numpy&suite=unstab... (the grayed out archs are the ones non release critical, so packages are built as best effort and if missing is not a big deal)