Although super easy to make if you own a food processor, all the Asian markets in the area carry these bases. I have purchased them at Hong Kong Market (Walnut in Dallas/ Garland border) and Super H Mart in Carrollton, to name a few of the larger purveyors.
I have purchased a nice green curry in the past that is packaged in a little tuna can sized tin. You will also see other curry blends, and they are pretty much the better quality I have tried. Not many choices so it will be obvious when you see them. I cannot remember the name off the top of my head.
Maesri brand curry paste comes in small tuna like cans that DallasDude is referencing. I have had very good success with that brand. Just don't forget your coconut milk, palm sugar and fish sauce for the recipe as the can does not call for it, but you will certainly need it.
http://www.maesribrand.com/114g.html - specific pictures of their small cans across the product line
I believe most restaurants around town do use the canned curry pastes. You can tell by the uniform taste across all the restaurants and the lack of that fresh flavor in, for example green curry, which utilizes kiffir lime rind, shrimp paste, galangal, just to name a few. Just those three ingredients alone in varying measurments could throw the taste in one direction or another. I would highly suspect that all Thai chefs are not going to have the exact same recipe for green curry to make the uniformity in taste.
My choice in locating the Maesri brand is Carrollton Plaza in Carrollton (it is closest to me in Lewisville). It specializes in Vietnamese products but they also carry Thai ingredients. Most Vietnamese themed stores will have the Thai ingredients like the following stores: Saigon Mall in Garland, Hiep Thai in Garland, Saigon Taipei in Garland, Hong Kong Supermarket in Arlington or Garland, and several other in Irving and Garland
Super H Mart (a Korean store) in Carrollton does have the paste but they are more expensive than say a Vietnamese supermarket.
Expect to pay roughly $0.75 - $0.90 per can....each can will make a large enough meal for two people if you follow the directions on the can.
Here are a few pretty authentic Thai recipe websites:
Key ingredients are the fish sauce and palm sugar as it is a balance betweeen sweet and salty (the US prefers sweet, Thailand salty).
If you are really into it I would suggest trying to propigate your own Kaffir Lime tree, lemon grass, holy basil, ginger, turmeric, etc. Many items, especially the Kaffir Lime are seasonal and the price jumps dramtically, even for the leaves.
List of the most commonly used Thai herbs:
In my experience Thai dishes are a bit more complex flavor wise than Vietnamese. If you are into Thai cookery then a jump to Vietnamese would not be a difficult task.
Got any good home made paste recipes? I have experimented some, but never turn out right. I end up just buying the store bought paste.
One note from a Thai friend about making curries --- the difference between a "good" curry and a bad one is when they add the coconut milk. In a traditional curry the coconut milk is first cooked in a pan (just the coconut milk) till the oil separates. Take this mixture off the heat and reserve for later. That is, don't just add the paste and the coconut milk and all your protein and veggies, but rather be sure to cook and remove just the coconut milk first.
Another trick is to get fresh coconut, shave it and squeeze out your coconut milk in a cheese cloth.
I suggest looking at the cookbook The Best of Regional Thai Cuisine by Chat Mingkwan. It has some pretty authentic preparations for curry pastes and other dishes as well as giving the differences between the culinary regions in Thailand. That should help you on your quest for good curry pastes.