That is my favorite sound. My girls will sometimes squeak during playtime or when they are on their wheels. Shelly will do it when she sees me. She knows how to get my full attention.
Off the top of my head, I can't think of any breeders in the immediate area. Also, how far are you willing to travel (mileage). This is Los Angeles, it can take over an hour to drive from the Valley to the West Side.
The sharpie trick on the ear will work. Give it time. You will get to learn their personalities. They may look the same, but I swear they all have different little attitudes.
I have never heard of those brands. My girls eat Oxbow. If I could buy larger quantities of it, I would. Personally, I stick with what I know and what works. :)