Try the waistband and elastics page on Apparel Search. I am actually trying to start a new site to help everyone find trimming, but the site is not yet active. The site is called the Trims & Notions Directory and is found at www.TrimsNotionsDirectory.com Unfortunately, that site is almost useless at this time because not many companies have added listings yet. It is free to list a company, but companies have simply not found the site yet.. If you know any trim suppliers, tell them about the site...
You can find more trim at the apparel components section on Apparel Search.
Hopefully other members will add suggestions for you. Good luck.