The best-known source for parts would be Hitchcock's in England.
http://www.hitchcocksmotorcycles.comThey have online parts books for most models.
You'd want to check the book that covers 1956 700cc Meteor. That will have all the engine parts you need. If you need fenders, the English made Meteor parts aren't the same as those used on the US market Indian Trailblazer.
In the US, Baxter Cycle has parts, but you'd need to call them because their online store doesn't list the Enfield parts.
Beno Rodi in Atlanta has a lot of parts as well, and he'd also need a phone call.
Both Baxter's and Beno Rodi can be found online using google.