I don't know of a source for 'vintage' 26" tubulars, but whenever I google search for 'panaracer rapide tubulars', i always end up hitting the wheelchair racing supply shops which have tubulars in a zillion, zillion sizes, e.g. :
etc. etc. I wonder if these bicycle wheels were actually 'borrowed' from the wheelchair industry ??
- Don Gillies
San Diego, CA, USA