To get Green Top for ranch follow these instructions.

1. Hold your controller so O is pointing your north.

2. Press X with your first finger extremely fast.

3. You will reach a point where the Green Top Slides then press X and R2 as fast as you
can and it comes loose.

-My Youtube Channel.
-BoyFromBolton

For the walkthrough guide
I reccomend you type "tony hawks american wasteland walkthrough part --" the guy xxSk8erxx
who made the walkthrough does a fantastic guide through the game.

Hope i helped -.- =D

Im sorry i dont know its probably a bug in the game