Red chili paste (aka red pepper paste) is one of the most recent - still dates back to 1700s though - addition to Korean condiments, made with red chili powder, glutinous rice powder, soybean pastes and few other ingredients. In fact, red chili powder was first introduced from Japan shortly after their invasion of 1592, and was spread in Korea throughout the 1600s. In other words, there was no 'red' kimchi, as we know today, to be found anywhere until 1700s.
Koreans like to talk about this seemingly interesting historical fact. Considering how much Korean people love spicy food and kimchi is the important national foods, it's surprising to know that 'red' kimchi has only existed for the past 400 years out of its 5,000 year old Korean history. This could be a little disappointing, I think.
Anyhow, red chili paste is easily found in any Korean market. In fact, you will have a harder time making a decision on which one to buy. My mom recommends Soonchang Gochujang (Gochujang means chili paste) made by Chung Jung Won, shown above. It is the safest bet, I think.
It is so cool ~ Wikipedia even has an entry on Gochujang.