I had just researched this a couple of weeks ago- I did not find anyone in the us who sold concentrations greater then 100mg/ml.
The one I bought from was the one I found that was the cheapest for 100mg/ml Arctic Vapor who has 125ml for $42 - I have used it for mixing and was very pleased with it. It arrived in 4 days in a dark blue glass bottle that was packed extremely well, too well actually as the foam and bubble-wrapped package was at least 4 times larger then needed.
I have also bought from blue mist vapors before- though the e-
juice I bought from them was a lesser concentration - I would not hesitate to recommend them - well packed and shipped, quality products their price for 125ml of 100mg/ml is $55
I also checked out MyFreedomSmokes and xtremevaping but have not bought from them because of price - both sale 125 ml for $58.95
But, if you don't mind waiting a few days I read a post this morning where they are puting together a coop to order a large volume from blue mist vapors at a discount price only $37 for 120ml - ( you can
buy smaller and larger - I was just picking similar sizes for price compare)
here is the link to that thread:
http://www.e-cigarette-forum.com/forum/pif-co-ops/125649-100mg-nic-juice-co-op-mod-approved.html