Wanted
Hi. Assuming you are UK based, you may be able to get one from Maplin's, RS Components, Farnell. if you Google you will find their web sites on the internet. However there are many 27MHz transmitters being sold cheap for about A£5 and if of the same type with a good aerial this may be your cheapest option. if the set is good it may work with your receiver. if not you may need to modify the mounting as some use a male or female connector and the very early type had a spring clip. Modification should be quite simple as the main criteria is an electrical connection between the lead from the circuit board to the bottom of the aerial. Try Howe's Models or a car boot sale. Good luck.
Dave
Live long and prosper
Dave