Well, I have gone with a budget approach for now. I obtained 16 Kodak disposable camera bodies free from a local photo dept. They usually recycle them, but were kind enough to allow me to have some of what they had. They will have either 120uF 330v or 100uF inside. ^^ I will let you know what I find. Then I can add 4 more to the first stage for ~1550uF. I should have enough left for ~1200uF in the second stage. ;-) I could get a few more of these camera bodies to reach the 100J first stage and 50J second stage that you recommend.
Also I'm curious as to what would happen if you asked your photo processor for disposable camera bodies? Is it possible to get them in Germany? I know you prefer to purchase larger caps that are low esr for your designs though.
Edit: I have a length of "C" channel aluminum 78" x 3" x 1", and I'll have to be creative designing the frame using it because 3" is a bit too wide. It's not a "hard" alloy and cuts reasonably well with my hacksaw, just slow and tedious.
Another 4 caps were added to the single stage for a total of 1550uF. It was able to penetrate the front of an aluminum can fired at it point blank, with the flat ended 6mm x 3/4" projectile. If it had a point on it, then it might go through both sides of the can. Therefore I have ~70 Joules so far. I will have to add about 5 more 120uF caps to reach 100J, after I get some more disposable Kodak camera bodies.