If you do pick some up at TSC, make sure they do NOT also contain the vaccine for equine flu. I've never been able to get mine at TSC because I've never found vaccines that don't have that tossed in.
Reason is, if you vaccinate them with that, they'll start making antibodies for bird flu. And then if, for some reason, they were tested for bird flu, like if you had cases in your area and they were going around testing backyard flocks, it would test as positive, and they'd put all your birds down.
If they contain tetanus toxoid vaccine, that's fine, birds can't get tetanus so it does nothing for them but it doesn't hurt either.
I was also gonna ask if you thought he might have gotten into something he shouldn't have, and this may be the answer. I'm not sure there's much you can do aside from wait and see if he gets better, if this is the cause. I can't even recommend a charcoal flush because you shouldn't do one if cyanide is involved.