Eldi,
There are several "very worthy" cab builders out there. Kress,Mojotone to name a few.Do a Google serch for each(as I'm too lazy to post the web sites).
Kress and Mojotone do 'spot on" Marshall cab reproductions ,all with 13 ply marine birch sides,back and baffles.
Kress sells a 4x12 empty Marshall'ish cab in any color you want for about $ 350.00. Mojo is a bit more pricey.
Do this as well. Go to E-Bay,under amps, type in "4x12". Theres is a dealer that sells Mojo empty cabs at a really good "buy it now" price,($350.00) and shiping is like $50.00.
Hope this leads you in a direction that can help.
Peace,
~ John ~