I only keep spare piston springs, small bolt parts and a firing pin in my range kits. I don’t even care about the charging handle assemblies much honestly, the old ones die but it takes a lot of work.
With that being said, there is no real f part number for the charging handle assembly. I’ve tried to order them a few times and never received any parts at all. Anymore you have to order the new spare ambi assemblies. I have a few in stock now.