I inherited an 870 Wingmaster in 20 gauge, and we found the gun apart (maybe for cleaning?). Long story short, I appear to be missing the whole trigger assembly, including the retaining pins. I'm searching for something to replace it, since a) I want this family heirloom to be a complete firearm and b) I'd also like to shoot it

But I'm having trouble finding thing with the exact details (Wingmaster 20 gauge). Most just say 870, nothing more specific. Are the trigger assemblies generally the same between models and calibers? Or do I just have a special snowflake of a shotgun that I'll have trouble finding parts for?
Any help will be appreciated, especially links to any places to buy the right parts

Thanks guys!