One could always make one from an XS750 base and weld e.g. an SR500 top onto it. SR500 tanks with rotten bottom shouldn't be too hard to find and you have an XS750 with a dent (the one I gave you a few years back).
I could throw a TR1-Tank onto my XS frame and see if it'll fit. If it does, the Mojave will as well, as everybody and their dog does it on XV750ies.