M frames of that era came with 2 different headtubes.
Lower end had 1in (or 1.125, i cant remember) , and the more expensive ones had 1.25. So you'd need an evo threaded headset.
They do come up on ebay, but tend to be bloody expensive!
look on retrobike and see if anyone has a pepperoni fork for sale.
2 things to be aware of these frames are:
top tube bowing due to poor heat treating
if it came with suntour originally, a lot of chainstays wore away due to a lack of clearance and a flexy hub.
Its probably pushing its limit of age for an alu frame so be careful