Mmm perhaps, I don't have one spare to try though.
I emptied out my nuts&bolts into a casserole dish (!!!) and picked through it - out of about twenty bolts I tried, I found one that was the correct pitch.
Tomorrow I'll go down to the hardware supplier and see if I can get some in the right size, and then I'll take 'em down to the workshop and see if I can drill them out to make my own adjuster.
Also, has anyone got a spare steel jockey wheel for one of these? Mine has one original steel one and one replacement nylon one - ideally I'd like them both to be steel.