Telephone (or visit) a military tailor that makes RAMC mess kit and ask them to send you a piece. With any luck they will send you an off cut for nothing or next to nothing but beware many of these people would sell their own grannies.
Slightly off topic but does any one know why officers (and WO1s) don't have dull cherry backing. It would not be difficult to make the badges in dull cherry. I suspect the reason may be that nobody thought of it at the time but maybe there is another.