How about just go to the source (manufacturer)?
Mongoose Contact Us They may be able to give you the required specs, and perhaps sources. That being said, from pics I pulled up it appears to use a cartridge type bottom bracket (would need to know proper spindle length) probably a "square taper" type, and you would also need to specify crank length. Pedals are standard 9/16" - whatever style you want.

Depending on how much is missing (cranks, bottom bracket and pedals?) this could end up costing you quite a bit, so I hope you paid very little for the bike, which sold for less than $200 new, worth well under $100 used in rideable condition.

I’m happy to help further over the phone at https://www.6ya.com/expert/donald_f2ed37026a3ac881