I have been impressed by Capital Aquarium in Sacramento. I am not sure they know Loaches, but they are the best store in that area. On the other side of the freeway is a little hole-in-the-wall aquarium store, O Street Aquarium. The fish are well cared for, and they carry unusual fish.
http://www.capitolaquarium.net/
http://www.ostaquarium.com/
In Dublin is a store where one of the employees is very interested in Loaches. The store is Aquarium Concepts.
My problem with them is that the nitrate in their water is very high. I think they fight it by adding salt. It takes a month of acclimating to get the fish ready for my main tanks. This is a typical quarantine period, anyway, but I sure would think it better that they deal with the nitrate some other way.
http://www.aquariumconceptsinc.com/
The other place that is worth some phone calls, and a visit if you are near is in Campbell. Dolphin Pet village. They have a really big selection of fish, I often see Loaches, and many different or less common species of Cories, Rainbow fish and many more.
http://www.dolphinpetvillage.com/
Look for a coupon at the Dolphin web site. It is not always there.
38 tanks, 2 ponds over 4000 liters of water to keep clean and fresh.
Happy fish keeping!