Ruger 77/50 De-conversion?

My Father in law just got Ruger 77/50 from a friend. It currently takes the 209 shotgun primers. From what I've read online, this means it was converted aftermarket, as Ruger never sold the gun with a 209 breech plug. The small ring on the breech plug that holds the primer in place has corroded away. Since he uses #11 caps on his other muzzleloading rifle, we're interested in converting the 77 back to "stock".

I've been tasked with finding someone who has converted their 77 to 209 and still has the original Ruger breech plug and firing pin and might be willing to sell it for a fair price.

If anyone is able to help, please, let me know.

Thanks!