contact bontrager/titec - maybe they could send you a replacement.
as you know, the part you are looking for is a semicurcular piece of tube with grooves for the rails
Normally, that would have been exactly what I would have done. However, I can't find Titec as a company on the Web! Can find plenty of resellers, as well as Madison as their UK distributor and Belda Bikes as their distributor in Chile, but not actually Titec themselves. Does anyone know if this is a brand name that is manufactured by someone else? Do they actually still exist?
I've dropped a line to Bontrager, but suspect that is a very different company from that of 20 years ago and probably no longer has the parts...!
Rossin Concept MTB 1990 - Full XTR M900
Litespeed Ocoee Titanium MTB 1992 - Grafton / Bullseye / Syncros / XTR
LeMond Z Team Issue SLX 1991 - Full Corsa Record / Sigma
LeMond GAN Team Issue GLX 1993 - Full Dura Ace (7400)