I'm guessing the Mare's Legs suggestions aren't on the compliant list(s)...They aren't semi-automatic so the elements of the AWB shouldn't apply.
Okay wait...I have an idea and it's fucking crazy but hear me out.
I just looked apparently hand guns made
prior to 1998 don't have to be on the handgun roster, right?
Inglis Hi-Power -
https://www.gunbroker.com/item/870723501
Broomhandle Mauser 'Red 9' -
https://www.gunbroker.com/item/872178239
Artillery Luger -
https://www.gunbroker.com/item/872107369
I know it's absurd...but
1) Shoulder stock
2) detachable mags (in the case of the Luger and HP)
3) they are not SBRs according to the NFA (being exempt under C&R eligibility).
4) Legal to carry on your person under a concealed handgun act.
5) Exempt from the MA Roster Requirements.
No law says you have to use the stock Inglis upper and barrel or safety on your gun when shooting it. You could get an upper built, dovetailed rear sight with a MRDS dovetail and use an RMR/DPP, use an updated thumb safety...I bet you can even find pre-ban high-capacity Hi-Power magazines...