Brownells carries two differant ones to replace the ISS unit , one is a Remington made pin spring and rear shroud and the retail price is $48 dealer price is $38 the part number for these are as follows
Stainless Short action - #767-000-064
Stainless long action - #767-000-063
They also carry a unit made By Greg Tannel which in my oppinion is a much better replacement and well worth the few extra dollars and the bolt shrouds are made from aluminum. Retail price is $65 and dealer price is $49 the part numbers are as follows
Silver Long action - #100-000-446
Silver short action - #100-000-447
I have replaced all the factory rem firing pin assemblies with the Tannel units wether they had the J-lock or not