Or contact Airfix - they have always operated a free, replacement parts service, and used to include a simple form in every kit box. You just need to quote the kit name, scale and part number, and the reason for replacement. (In this case, the part isn't lost - it's broken, or was missing from the kit or ...)
Address is :- Hornby Hobbies Ltd.,Margate, Kent CT9 4JK, United Kingdom.