Dave, the Edinburgh coin is the most difficult to acquire I believe. As a set, you should be looking at no more than £6 + postage if you really can't wait for them to turn up in your change.
If you like to play on Facebook, see if you can join the group "English coins for sale and wanted" and ask on there. You should be able to get them pretty quickly.
Personally, I would rather wait until they turn up in my change. I got a Belfast one yesterday.