The one thing I would suggest is if you can't find a
cavy savvy vet is to find one that is willing to learn more about them. The vet I go to didn't start out as a small animal specialist (at least that's what I've heard), but she was willing to listen and learn from people that run resuces and will always look up information if she isn't sure of it.
I also take printed pages from guinea lynx if I think I've identified the problem and will show them to the vet if I think they aren't doing/looking at the right thing.