I have a load of spare parts that I'm about to get rid of. You could
make a 3U case out of them. You're more than welcome to the for free
(depending on postage). You would need to supply you own power
supply. Let me know if you want these. PS, anyone else wanting
non-Pro-ma, but Doepfer compatible profiles and sides, let me know.
May require a bit of tinkering to fit, but I have used a lot of this
stuff in my old synth cabinet.

Yours Aye

Stuadh