i got a way. make custom researches. set those research id to integer array.
so, level 10 item research level might be itemresearch[10]. make the trigger do, a hero gains a level event...it'll learn him itemresearch[getherolevel]. and make the items that require level 10 requre the tech.
i think this method merely prevents buying...i'm thinking it does nothing to prevent pickup of items...so if an item drop requires level 10...you might be able to use it if you're level 9. i haven't tested this yet, though, it's just a guess. but obviously it shouldn't be hard to control what items are dropping depending on the hero level...if those items would even be allowed. it's just that if it's a multiplayer map then a guy could get level 10 faster than other players, and buy the item for his buddy that wants it who is lower level...that could be an exploit.
like i said, i didn't test how the requirements work on items yet. but i'll do so soon.