Sorry to read this frustrating thread Mike!
This might be of interest to you, probably worth a visit as it's in Wales I believe, so reachable for you. It's a very skilled lady who makes the tanks.
I know she has made tanks to fit Monster frames, but probably not Monster tanks as such.
Nothing looks like it phases them though and well sub £1000 for a bespoke tank, with your spare as a pattern.
https://tabclassics.com/