toy joy might have some stuff vaguely suitable (long shot, but maybe worth browsing). otherwise the toy stores are pretty standard fare and hobby places aren't very specialized. used to be a place on south congress that had interesting out of the ordinary stuff (can't recall the name).
it's been a long time since i lived in austin, though, so not sure what might have cropped up in more recent years. if you're looking for older stuff (gi joe, etc.), i would go to the ginormous antique mall in Pflugerville (if it's still there). there were always dealers booths with older military toys when i visited (granted, again, this was 7-8 years ago).
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