Does anyone know of a source for firing pins for Ruger Gunsite Rifle in 308?
Ruger does not want to sell the firing pins. They say the rifle has to be sent
to the factory for fitting of the part. I like to have an extra just in case of
failure.

I would not sweat it. I’ve been a gunsmith for as long as a Ruger 77’s have been out and have yet to see a broken firing pin.