Try to look this on Ebay.
https://www.ebay.com/itm/Rawcabs-Boogie-mark-IIC-and-mark-IIC-head-cabinet-1989-vintage-mark-III/302779358702?hash=item467f0e5dee:g:rlIAAOSwPh5ZMe5c
I've built a Mark III head shell recently, and others in the past, and a lot of guitars. I'm certainly capable of doing it for you. Full dovetailed joinery in hardwood, softwood, or plywood cabinetry, with or without reverb tank cutout, pretty much any way you want it.
I have access to at LEAST 140 different patterns of tolex and leathers, too.
www.kayline.com is the manufacturer of most coverings I have ready access to, but I get their products through distributors. Kayline shows samples of everything they offer, on their site, and even if you want basic black tolex there are several choices to choose from.
I'd be interested in taking the job on for you. Feel free to email me at [email protected] if you're interested.