Where to find pressure treated wood?

[new2chickens2011]

Building my first coop and....I'm trying to find pressure treated 1x3's and 2x3's but it seems everywhere I go they only have 2x4's. Any ideas?
Thank you!

 

[dawj]

Good saw blade in table saw

Rip them in half to make 2x3's (2x6) and rip the deck boards in half for 1x3's they are 5/4 x 6.