Start here:
http://www.adga.org/clubs.htm#IN
Call them, and ask for local contacts. You might consider an older (but not geriatric) doe. The way I see it, a serious breeder does not have room to hang onto so-so does... so, any doe that has been kept long enough to be possibly replaced by a kid/grandkid is a doe that earned her place quite well. Arrange to freshen her with a quality buck for replacement/additional does.
Also, check the website of the breed club for the breed you are interested in.
http://www.adga.org/breedclubs.html
Check their membership directory, and see if there is a local member you can talk to.
Another place you may consider checking are the local 4-H/FFA clubs. A parent is likely to be very helpful in finding you a good doe, especially if they have seen the "keeper" list of this years kids steadily growing longer and longer ;-)
Call classified listings. If they show their does (and/or the does are from good milking stock), they probably know other people with quailty stock. If you see a listing for dairy goats, but it's not the breed you're looking for...call anyway. There's a chance they know someone that has what you're wanting.
Be clear about what you're looking for! I got one of my LaMancha does and my dairy ewe by calling on ads that listed kids or adult sheep for sale. Neither were originally for sale. Anyone that has kids has does also and if they have does, there's a chance they have considered selling one but just never got around to it. In both cases, the ad was for the breed I was looking for, but not specifically what I wanted (ie, looking for adult doe, but listing is for kids). It never hurts to ask.
Good luck with your search!!
Liz