I'm sure you have already looked at what we have at Rings & Things and probably at Leather Factory / Tandy? Some of the southwestern suppliers have things that work with bolo and belt styles that are popular there. (Rio, Indian Jeweler's Supply, Thunderbird Supply, Sante Fe Jeweler's Supply)
I used to get western design findings from a place in NYC that serviced the fashion Industry. They had a number of parts for leather outfits, bags and purses. The name was Eslin, Eselin, Eslinger or some thing similar. A quick search in Manhattan yellow pages did not find them but perhaps they have moved out of the CIty.
What particular items do you need?