Shoot one measly mourning dove and pick all appropriate feathers from it. Easy. Then eat the rest or feed it to a good hound or kitty. Songbird schmongbird.
Feather holes aren't this hard. Retaining a feather in the feather hole isn't that difficult and I usually keep an extra feather or two in my hatband or bag. Starling feathers might work too, but as I keep them runnoft, i don't have access to 'em. Yes there are other unprotected and game birds with an array of touch-hole sized quills.
I have seen originals with double feather holes, and I'm thinking I might double mine. Momento por favor--
Mine is about 5/64 as best as I can measure at present. I think it's a little bit tight on them, but I've never lost a feather out of it-and it's the only size I've tried. I probably put it in with a gimlet. I don't recall ever seeing a dimension given, nor have I measured an original.
My touchhole is quill-blocked any time the pan isn't primed and there's a charge in the bore. I may drill the feather hole out a few 64th's more and some deeper, and add a twin because closing the pan on feathers rags 'em out pretty fast, And I'm seen at least one two-hole original.
I think I've seen as many with inlay as without, but of course that little gun needs a bit of silver 'round the feather hole.