Hi Ken good speaking with you agine. I believe Central Hobbies is the only major supplier of Tetra but not sure perhaps some of the cottage industry pylon specific suppliers do. Anyway here they are and be careful they also sell Tetra conventional tanks that look almost the same so just be sure you order "Bubbless". They are not cheap but for controlline or some problematic RC types especially throttled engines they are more than worth it.

http://www.centralhobbies.com/Fuel/fueltnk2.html

John