I've been in West Marine and Boat US stores that carry stock....not sure if it's to your spec. I also have a few teak fabrication contacts in FL I've used for custom work and stock teak trim. I'll do some digging and try to find if you're interested.
Thanks for the heads up on teakmarinewoodwork. I bought some mahogany and fabricated my own rails. The mahogany was $10/board foot vs. $34.50 for teak. The mahogany is stronger and more rot resistant but much harder and more difficult to work. Color is darker (more reddish) than teak.