Yeah, not exactly "Portland", but this forum has a decent list, that's how I found some.
Oregon Outdoor Shooting Areas
Information and discussion on where to shoot for free outdoors in Oregonwww.northwestfirearms.com
Well, yes, that's back to free areas. I was trying to think of a range or club that might work for you. I don't think there's any right there inside Portland geographics.