Can anyone help! Double ended studding size.

I have a 1988 Spider 2 litre. The stud in the front of the water pump that holds the support bracket for the alternator has dropped out! Feeling with a cocktail stick the thread appears to be fine and the hole is quite deep. My problem is the thread size of the hole in the pump. I have tried almost every bolt in my workshop and also a mates, no luck. Any advice for a source for the stud or a bolt with the correct thread would be greatly appreciated, especially now the weather has changed. TIA Dave