I loved how the MAC prochamber sounded on my fox and was looking at getting one for my 97GT I picked up last year, but I cannot find anything on MAC anymore. Did they go under? I was also having trouble finding any off-road midpipe for this car.
The EPA cracked down on exhaust manufacturers heavily a year ago and issues lots of fines, which caused all to cease producing off-road H-pipes. You might be able to find a small-time manufacturer making them, but only because the EPA hasn't set their sights on them yet.
If you find one used for cheap, scoop it up. Once it gets out that bolt-on off-road pipes are no longer available at all, the pricing of used ones will shoot up