You could probably make a replacement if you cant find one anywhere.
You would need to make a mould in something like plaster of paris of the one you have. Do half at a time so you can make sure you can get the original part back out. Then once you have the mould you could fill will low melt temperature plastic. You can get it on ebay and amazon.
3d printing would be the best bet but it can be done by hand if necessary.
If we can get hold of the part I can get a drawing done for the 3D printing any format . May be some one can lend you one
And here's one I made earlier...Stu you make it sound so easy, you should be on Blue Peter...