You must not have used Google when you looked all over the internet because TW Metals is one of the first links when you Google 7075 aluminum tube. I think what you meant to ask was if there is a place that you can buy a small amount. I have found several places that have it but am yet to find a place that sells it in a smaller amount than 20ft. Just get yourself some Titanium. Titanium Joe.
http://www.speedymetals.com/default.aspx you can buy by the foot.
7075 is stronger but does that make it safer? Perhaps but consider this. 2024 has a larger margin between tensile and yield. This will give a much better chance at a soft failure if there is one. Even at 3000psi, you would have a 3x saftey margin using 1-1/4OD with 1/8 wall. I would tent to lean toward the 2024 unless I was going for pressures above 3000. Of corse I didn't take into consideration thread root as he thinest area. I tend to like the way Edgun and Cricket afix their end caps ect. thus I didn't consider thread root. Something to considerBill