i usually look on ebay, there are some great bargains to be had there (once you have waded through all the nonsense: e.g. folks bidding upwards of £100/US $150 for a Dunhill estate which has obviously seen better days)...I got a lot oy new Petersons from ebay a while back, from a vendor called "estore4" or something like, who was in WA (Seattle or Spokane I think, but I forget)...also I have a great tobacconist in my town who stocks a nice range of Falcons and Petersons....I also restore and sell pipes on ebay myself and I usually list a few each Sunday, from Dunhills to Petersons to Savinellis and everything in between....
so yeh, ebay is a good place to start