Don't blame UPS, it is the outlets that have there own policies. Some outlets are gun friendly and some are not. I have one guy that thinks everything I send is a gun. He is a great guy to deal with, and I have everything packaged up before I get there, and the shipping paper work filled out ahead of time.
UPS will ship it, it is just getting the anti-gun outlet stores to package them up. Remember, most of them stores hire people off the streets, and when they are told the rules, they just make it easy on themselves and don't allow any guns.
Contact the outlets manager and see what there police is. Then find one that is gun friendly, and only use them. Package it up yourself and tell them you are shipping parts.