We buy most of our GF items over the internet.
http://www.kinnikinnick.com/ and
http://www.glutenfreemall.com/catalog/index.php are ones we have used, but there are others.
As for transforming to a GF kitchen...well, we're only partly gluten free, as the only celiac in the family lives with us only part time. However, I started by learning how to read ingredients labels to identify foods that may contain gluten. I also used a lot of the mixes and the few items in the grocery stores marked "gluten free." I also stayed away from flour-based foods and packaged foods that aren't labeled gluten free, and stuck with safe foods such as meats, veggies and fruits.
The one thing that made it all much easier was learning about GF flours. I now have a favorite mix
recipe #149852 that I use as an all-purpose flour. When a recipe calls for flour as a thickener, such as most gravies, I usually substitute corn starch. For everything else (except baked goods) where the flour is more than just a thickener I use the all purpose flour mix. I've had great results with it, and have found it works well in quick breads. I've never tried it with yeast breads, cakes or anything else that requires exact measurements and specific chemical reactions. I've found that it's best to use recipes that are formulated to be gluten-free for those items.
The one ingredient that causes me the most grief in packaged products is "modified food starch." It may or may not be derived from a gluten-containing food, but we can't take the chance. This is where label reading is important - I usually find that, if that is the only suspect ingredient, if I read through the labels of the various brands I will eventually find one that says "modified corn starch," which is safe.
I only converted to GF cooking a couple of years ago, so I'm really still on the learning curve. I'd be happy to answer any more specific questions you may have, but I'm sure that those with more experience will come along.