The collision polygon isn't accessible from just events. That said, you can manually put the collision point locations in an array or something and just reference that instead. Or you can use a tiny sprite to find the collision shape by moving over an area and checking for collision.
I think that's pretty good.
Set yourself some image points in the sprite.
Check if collision sprite player with tilemap.
If have a collision, placed a small sprite in every image point and check if collision occurs tilemap at that point, then you get that image points have collision.