the acetone 'melts' the ABS plastic by partially dissolving it into a goo, but a single or even several layer print even at high temp is still only as strong as the contact points of the squirted plastic. It just requires being realistic and often printing a multi-piece part which is glued or fastened together. Even then a printed part is (using current FDM or UV cured resin tech) not going to be as strong as a nice hot 100% fused injection molded part.
There are hacks which require several steps starting with a CAD design and FDM printing resulting in an Aluminum mold and then doing injection mold but not terribly practical for a cover which will probably require several iterations to get it right.

As for Mugen covers, they had a $5 sale on ebay areoud 2011-12 when I got mine, I am keeping it for experimental builds. I have not seen since and their website last checked a few years said not in stock.