There seems to be more to irony than just being unexpected. If I'm playing poker and get dealt a straight flush, I wouldn't describe that as ironic unless something about the context made that particular hand notable as well as unexpected. For example, if we'd just been discussing hand odds. The bit in the song about the guy who avoided flying his whole life to have his plane crash seems like irony to me, though.
If you found a couple of spoons when you searched for a knife, that would be merely frustrating ("damn, where's a knife when you need it?"). It's also close to what you'd deliberately expect ("I either find some knife, or I find some other cutlery but no knife").
Getting 10,000 of them but no fucking knife is not just frustrating but also ironic -- and outside of expectations.
It agrees to a T with:
"a state of affairs or an event that seems deliberately contrary to what one expects and is often wryly amusing as a result"
One would expect to either find the knife, or find a some other cutlery but no knife.
Chancing upon 10,000 cutlery items and ALL of them being spoons --just the kind you don't need-- seems both "deliberately contrary to what one expects" and "wryly amusing".
(Note that it doesn't have to BE "deliberately contrary" -- just to "seem" so, e.g. as when you feel that luck or the universe conspires against you).