Hi Graeme / Barnes (love the bass on your profile pic btw, Barnes).
Thanks very much for the advice.
Hi Mica - thank you ever so much for that. I really appreciate it. I had spent some time today trawling around modelling shops and the like as they seem to stock similar things for radio-controlled cars as it happens (hardware stores in London hadn't anything), but you're correct - no joy with that exact size when I was matching another of the remaining screws with what I could find.
It's very kind of you to send me a couple - I'll drop you my address now.
Thanks again for all the help.
Best wishes
James