How to get alternative shiny leaf for Route 33?

Question

I have a Fire-type Pokemon with a Serious nature, and apparently there's a shiny leaf on Route 33, but I've found out that Fire-types can't get a shiny leaf on this route.

Comments

Edit: After a few resets it turned out that my Pokemon needed to find the shiny leaf before it got mad at me.

Answer 1

Shiny leaves depend on the Pokemon's nature, and the route it is on. To my memory, it had nothing to do with types, and is solely dependent on nature/ route match up. Also, since the leaves are so rare, you are not guaranteed a leaf even if your Pokemon's nature matches with the route.

Here's a table showing the nature/ route match ups:
Bulbapedia on Shiny Leaves

It's a bit too long to post here.