Thanks for replies.
The top is not curved, but I can see what you mean. It is an optical illusion, it is flat!
I find that "short runs" of anything like this would cost a fortune, plus postage on top of it. So not really an option for me!
When I had a small circular saw, I could indeed have made it myself. But the motor burned out (Dremel) and I couldn't find any circular saws of a similar size, and have no room for a larger one.
I don't have an electric plane, and don't really want to get one. (Lack of space, and another gadget to learn how to use). They have one at the local ship model club, but demonstrations didn't impress me overmuch! I think I will just have to find an alternative edging, but I doubt if it will look as good.
Some time ago, I had a similar problem with 18mm quadrant beading for the outside of the case. The manufacturers suddenly took to cutting the corner off, thus losing me the reference edge, and my woodworking skills were not sufficient to obtain accuracy without the corner. I tried cutting round dowel into four pieces on the band saw, and couldn't manage it with much accuracy. After a long search, I found a supplier of 18mm quadrant who didn't remove the corner.
Bob