I really don’t have much to say about Virago engine rebuilds. Rebuilding an engine is serious motorcycle mechanics, and unless you have the skills, tools, and experience (or are ready to just dig in and become a mechanic the hard way) rebuilding is best left to those who already have the qualifications.
Parts from Yamaha may well be available, but they can be VERY EXPENSIVE. You
can check availability and prices on www.bikebandit.com.
To find a mechanic who is qualified and who will actually have a interest in doing this job (particularly if the cases have to be split) maybe a challenge in itself and also very expensive.
If you are already an experienced motorcycle mechanic and have an understanding on how to do it, then maybe you go for it. Otherwise, look closely at the costs and the support you’ll be able to count on, and see if it makes sense.