Euphdude,
If you're still looking for Besson caps, just about any machine or metal fab. shop with a CNC machine should be able to make valve caps, finger buttons, water keys, etc. to order if you provide them with either a sample to take measurements off of or the proper specs.
In the musical instrument repair world, Dan Oberloh has made replacement Besson caps and finger buttons in the past, so he'd probably be able to do it again without much trouble: Besson Caps