I'm sorry to hear you're having a hard time finding a good vet? Have you tried contacting rescues near you? They may be able to point you in the right direction.
Kuufke & Knoevel both have vets that have gotten positive feedback, but they may be too far away from you? You can also try contacting Stichting Cavia, as they're more spread around the country.
konijnen has a list of rabbit vets around the country as well. If a vet is experienced in rabbits, then there's already a good chance they know enough about guinea pigs as well.