Actually,... for the
B-18A Bolo
Airmodel, Execuform, O'Neill, and White Eagle all made vacuform versions of the B-18A Bolo in 1/72 scale;
and...
Combat (now Roberts) Models used to make a vacuform version at 1/48 scale. Haven't seen it on their website, but if there's enough interest (and if they still have the ability to make the form), I'd think these guys might be able to get us a few if enough of us ask. Dunno fer sure. Would have to ask.
No one has made a plastic injection-molded or resin version of this plane at any scale.
...for the
DC-2
A number of manufacturer have made a 1/72 version and even a few at 1/144. Mostly vacuform.
MPM used to make a USN/USMC DC-2 plastic injection-molded kit (#72091) at 1/72, might be one under their Condor label they started in 1993.
Pioneer and RVHP both made a resin kits at 1/72.
As for conversions... I don't do conversions.