There have been items exclusive to Generation 2 (berserk gene), Generation 5 (gems), and Generation 6 (thankfully, loppunite is one of them). TMs, key items, and unobtainable items don't count. Please don't question my curiosity.
I've cross referenced lists from Serebii, Bulbapedia and Psypoke against each other and it seems that no usually obtainable items are unique to Generation 4 games. So no, is the short answer.
Also screw you Pal Park Pokeball