Here are some useful outdoor billboards mockup templates freebies for advertisement designer.
Details of these mockups:
72 DPI
Smart Objects (It means that it’s easy for you to change the  Adv. screenshot)
All billboard Mockups psd freebie created and released by Ahmed Adel
License info: according to the author, maybe it’s under CC BY-NC 3.0

Billboards Mockup Template Vol.1

You can download the template psd file from here: Download it for free
Billboards Mockup Template Vol.2

 Download it 

Billboards Mockup Template Vol.3

Download the psd from here

Billboards Mockup Template Vol.4

Download the psd from here

Billboards Mockup Template Vol.5

Download the psd from here

Billboards Mockup Template Vol.6

Download the psd from here

Billboards Mockup Template Vol.7

Download the psd from here

Billboards Mockup Template Vol.8

Download the psd from here