I had a custom clutch-bell made by this machine shop, that I found on aliexpress. If you're handy with a pair of calipers and a CAD program of some sort, you could draft up the file yourself pretty easily. Would probably cost about the same as the kit I linked.
Other idea, could you try and use...
You could try to use a helicoil to repair the insert you have. For some reason the only M8x0.75mm (turbo plug thread) kit I can find costs a little over $100... for that price you could just about have one machined anew.