The Empire ASA for the AXe fits the Mini, but they're over £70 new. Occasionally, they come up for sale second-hand (was one within last 2 weeks). Otherwise, try Mclovin's suggestion of the NDZ Threadsaver. Had one on my Mini, good bit of kit.
its called a Relay Regulator, im not 100% sure, but i may have an spare one kicking about in my kit bag, will look for you when i get home in a few days if your still interested?
I have a smart parts one you can have if you cover postage. I havent used it for years, so Im unsure if it works although should be fine. Contact me if interested.