gun parts corp has them in stock part number #8500. From looking at the extractor collar are sure that a standard 98 LR extractor will not work?
I am assuming when you say your rifle uses 7.62 x 54R you mean the gun uses the Rusiian cartridge. I am concerned about the case rupture.
Do you know why the case ruptured?
Was it old ammo possible damaged ammo. bad brass?
If the rifle was mine i would check to see if a standard 98 LR extractor would fit the bolt. If it does fit, please remember the extractor will have to be modified for the Russian ammo