That is one thing I don't like about UPS. The customer is the shipper, not the reciepent. So as a reciepient you have no pull with UPS. I am surprised UPS still has this asnine policy. Ultimatly you are paying the shipping bill so you are the customer.
So what to do? did you pay by credit card? That gives tremendious leverage. Since the charge went to Lewisport then it is time to call Lewisport and tell them that if the parts don't show up then you will have to have the charges reversed on your credit card. That tends to really wake lazy people up. Lewisport arranged the shipping, you never took ownership of the product, sale was not completed. UPS was arranged by Lewisport, the UPS problem is Lewisports. Lewisport was paid and trying to wash there hands of the problem. If they are suddenly not paid, they have there money on the line as they bought the parts that are now lost by UPS that they hired.
I consider the fact that Lewisport just pawned you off to there supplier and is trying to wash tere hands to be a pretty crappy pratice. There are times I don't mind doing it (I had a couple issues with a stroker kit once and it was easier to deal with the manufacturer and skip the middleman). But when that fails go back through the broker/middleman who was paid to handle the deal. They buy a lot of parts from the manufacturer and have leverage in getting things right. They also have the cash on the line as they did buy the parts and resell them to you even if they never touched the parts. Credit cards are wonderful tools for "goods not delivered"