Like this? http://www.casetronic.com/corporates/40-t1160.html http://www.casetronic.com/corporates/40-t1160.html Not ARM-based though, but they do have a varia

Like this? http://www.casetronic.com/corporates/40-t1160.html http://www.casetronic.com/corporates/40-t1160.html Not ARM-based though, but they do have a variant that can host 4 pico-itx boards: http://www.casetronic.com/corporates/42-t1040.html http://www.casetronic.com/corporates/42-t1040.html . I gather you may be able to convert that one easier to fit an ARM board, or RISC-V for that matter.