If you really just want one they do sell them individually in Japan which you can import from places like Amazon Japan or AmiAmi.Ok that's actually amazing.
The witch outfit is really good. Almost makes it tempting enough to get, but don't these amiibo only come in the three-pack? I'm not really interested in the other clothing sets.
Being able to save three more gear loadouts for quick access, though...hmm...
After shipping and possible taxes though it may work out better just to stick with the triple pack released in your local area lol