Bob,
A Mandarin Duck is raised as a domestic animal. Although I would be curious to know if they are genetically the same, to my eye, the plumage is identical to a Wood Duck.
Good fishing,
Arnie
Jay is readily available in the UK, from many dealers, but you may have trouble if you try to import into the USA. I believe there is a total ban on Jay over there.
If you want to try I’ll get back with a source, back in a minute.
Cookshill is one of the best suppliers in the UK http://www.cookshill-flytying.co.uk/p1welcome.htm
Once on the fly it is very very very hard to tell. Mandarin feathers tend to be a little larger and more golden. The most notable thing about them in the Black and White flanks. On a woodduck the B&W take up more of the tip where the mandarin has smaller bars making it very desirable for small salmon flies and wet flies. But because enough woodduck is shot before they are fully mature you are able to find B&W barring that is just like mandarin.
edit: alot at the time the book was written woodduck was illegal. This made all of the tyers of the time switch to the legal mandarin. Chances are if the book was written later or earlier woodduck would have been called for.
Joe Fox
Since I am tying for myself, Wood Duck will probably work just fine. It would be nice to duplicate as called for in the patterns, but as with salmon flies you just can’t get some of the materials anymore and have to substitute close as possible.
Mandarin duck are quite often raised for the table. I you can find someone who raises them or a small animal/livestock sale they are not terribly expensive.
I think you have gotten alot of good advice about the Mandarin. Probably on a fly it would be nearly impossible to tell Mandarin flanks from Woodduck flanks and Mandarins are raised domestically for food and because they are so beautiful. They are available but not really easy to find in the US. If you keep searching for one you will probably find one eventually.
Jay is a bit different story. As you might know, all of our native non-game North American bird species are protected by law and it is illegal to possess them (even if you found one dead on the side of the road). However, there is a Eurasian Jay that is not a North American species and they are offered from time to time in the US. Right now, there are a couple pairs of Jay wings in the US for sale on e-bay. People who deal in Salmon fly tying materials or who import the Cookskill materials into the US might also be able to help you there. Again, it is a bit hard to find but not really super expensive. I think there are some of the Bergman patterns that require JC body. That is pretty tricky to find. A couple want Bittern. I think that one is totally impossible today. Good luck!