The cat I had growing up was OBSESSED with olives. He would eat one, then roll around in the spot where it was on the floor. It was the same reaction he had to catnip, but more extreme.
My current cat is much less interested in olives, but loves catnip.
Try cutting and sanding a (too big for their mouth) piece of wood (it's a very hard wood), in my experience that's the most "potent" form of the drug. I used to keep a piece of wood, a bit larger than a domino, for my own cat and sanded it more or less regularly.
I don't know about olive species, but I know that not all cats have that weakness.
I've seen many cats lounging under (or on top of) olive trees in the Alps around Nice (France).