Yes.
If you have an old case on hand that you don’t need, that would work.
For I/O ports, I mostly used XLR-style ports, mostly by CLIFF.
For “user facing” I/O in the MK ii I bought something like this and threw the pci-bracket in the bin:
For my DIY-Case I used a Dimas Tech micro-ATX-tray.
For inspiration:
Build log of version 1
Build log of version 2
If you need less-common pc parts, Highflow.nl is pretty good.
If you need “not even pc parts anymore”, Digikey, Reichelt and other electronics-suppliers are a good source.