I found some Amish dairies somewhat locally by going to
www.manta.com and I've gotten a couple very nice older cows that were producing 4 and 6 gallons, and several people I referred to the dairy were able to get nice cows as well. I believe 6E got her Jersey from them and there was one other person from this board that I referred them to.
Here's a list of Jersey dairies in PA.
http://www.manta.com/mb?search=jerse...C+pennsylvania
The first cow I got had a high SCC in one quarter, she was older and was giving 4 gallons a day. Initially I was going to try to milk her but a large person with back problems and a small cow don't work too well together. That first night I had her I just left her in the corral with my 4 calves that had been bottled since birth and the next morning when I went out to try to 'foster' them onto her they'd already gotten everything sorted out and she mothered those calves like she'd given birth to all 4. She was very reasonably priced and worked out great for what I wanted/needed. The next cow I bought was giving 6 gallons a day and again, she adopted calves readily although she was younger and a bit more boisterous. Got a good deal on her too. They essentially sold her because I wanted another one, they raise their own replacements and had enough cows that they could sell a few of their older cows. They're like most farmers I know, never hurts to have cash in hand so selling off a few cows isn't going to destroy their business.
Still, though, do your research & maybe ask someone from a dairy if they would be willing to let you come out to the farm and show you what to look for without the suggestion of wanting to buy one from them specifically. The family I bought my cows/calves from were very nice and gave my 3 year old nephew a tour of the milking parlor and he got to see how they were milked (me, too, I guess, as I'd never been inside a dairy before, just done the home hand milking routine!) and all that jazz. Just very nice folks.