Like many pieces of “classic” hardware, they will be split between the ones collecting dust in a thrift shop for $5 and those going to auction for $500. To call it “widely available” would be a stretch, but the internet being what it is, they are not impossible to find either. Trying to find one without paying hundreds of dollars though… that may be tricky.
@dabbler I was multi-tasking under System 6.0.x (though it sucked, especially with only 1MB of RAM), and could actually have multiple applications visible simultaneously in System 7 without issues. I would say that multi-tasking stopped being a pain in the ass earlier than you think. Or maybe it just seemed that way since it was so painful under System 6.