Here are 2 cases that you may be able to use for a double power supply. The Thermaltake Core X9 is a solid metal case meant for pc's with EATX support. it modulair and you can probably fit a dual ATX PSU in.
The IPC 4U-4310L is a server rack with support for a redundant power supply. this also has hot swap ports and is a 4u form factor.
Both are not the cheapest cases that there are in the marked. but iBut I think that in these you can fit your pc.
So if you want a case with no hassle then you can get the Thermaltake Core X9. also this one looks the best and has good ventilation.
if you want a rack server you could go with the IPC one but it doesn't support 2 full atx power supplies but a redundant power supply (this means one set of cables etc.)
And if you want to go on the cheap you can mod any cube form factor case to fit your needs.
Overall i would pick the Thermaltake Core x9 because it can have an extra PSU install in at and if you get 2 it can get 4 of the badboys in there. also it's small so you can fit it anywhere with ease wich means hassle free installation.