I usually just go to a cafe and ask if they have cold brew (most do in Portland at least in summer), and New Seasons (local grocery store chain) makes cold brew all year round.
* Courier Coffee has probably the best cold brew in town on a regular basis.
* Barista is good, always good, courier is just ever so slightly better. They have it year round too which is a lifesaver for someone like me.
* Pie Spot actually has damn good cold brew on the inner E side.
Breakfast places with enough of a "hipster" (I don't say that as a negative, I probably am one, more just a way to identify them) vibe usually have cold brew as well.
In the summer, I generally consume a lot more coffee will more regularly make myself some. It's quite easy, you really just need a cheese cloth and some sort of bucket. Throw it in and wait ~12 hours. Last about a week.