As NJ said, most of use buy everywhere we can that is legitimate.
(had to preface that)
Our BST is great (you can save fees), ebay is great, the auction houses are great. It's a good time to be in the hobby in my humble opinion. The selection on the internet is mind boggling compared to what it must have been like in the 1980s and earlier, pre-internet. Personally I got back into it around 1996 so have been on the net pretty much the whole time. Good luck in the hunt (which is a lot or most of the fun to many, including me)