Haputanlas, If you hunt well, you should be able to locate some 1/6 bbl kegs without too much issue. IF we were closer, we could deal for two of the ones I have. I don't expect to be aging more than two brews at any given time. No idea what shipping would be on these things, but if you feel like trying to work something out on them, shoot me a PM...
BTW, the 25L kegs are 12" diameter, 18" tall... Small enough footprint, but the shape is such that they are not going to be easy to tip over. Plus, enough head room in them to safely brew even with really active yeast (for ~5 gallon batches)...