As for where to buy ram, the larger online retailers will have the best selection and prices, however, popular items may not be in stock and you will sometimes have to resort to the next tier. Places like newegg, zipzoomfly, excaliber (sp?), Komusa (A-Data), TBL, among many, are sources used by some of the guys that post here.
The point being made above with respect to your ram choice is that you should set a reasonable expectation for your cpu, then based on your 3.2 multiplier of 16, determine what kind of fsb you will need to achieve to reach that goal, plus a little bit of headroom so that ram does not limit your overclock. Select ram alternatives that will meet your speed needs and within the confines of your budget and ram availability, find the stuff that will run at the fastest timings. There are many makers of quality ram that will work with your setup, so before concerning yourself with a specific brand, concern yourself with what you want your ram to do. Only after you've determined your needs can you really make an informed purchase decision.