I'd second going to a breed-specific rescue. Sometimes, they acquire pregnant females and have whole litters of mixes. Not common but it does happen. Also, in my experience, some rescues are more willing to be flexible in their rules with older dogs versus pups. I work full time, so I don't qualify to adopt a puppy from many rescues. Before I bought my house, I wouldn't have qualified because for years I didn't have a fenced yard.
I live in Pittsburgh, and my shelter has mostly pit bulls, pit mixes, shep mixes. But about 2 hours away, in Ohio or West Virginia, I've frequently seen on Petfinder really beautiful collie or farmcollie dogs.