As for the 3" tubing you asked about some posts back.
I don't know if a american firm will interest you but this company can supply 3" acrylic with 1/4" (6mm) wall thickness.
www.mcmasters.com
Just look under plastics, they have many types and sizes offered.
I've order stuff twice from them & they are VERY fast in shipping to you. 2 day delivery the first time and this last time 1 day.
I'm impressed