A while on Typhlosion, but not long at all on Golem. The trick is that there's only certain routes, and of those routes, only certain of them
will have the leaf, and if you get one on one route, then if another route has that same type of leaf, you can't get it on that other route.
It's confusing. =P Basically there's five types of leaves, and at least one route that corresponds to them. If you get one in say, Route 1, and it shares a type with Route 48, you couldn't get another in Route 48 for that specific Pokemon.
