The list author says: "For the obsessive, every HG 00 1/144 scale model kit Amazon.com has to offer, #1 through #55 (plus a couple more!)
Amazon is a great place to buy these kits! I live in Los Angeles and have canvased the city looking for a good source. For price, speed of delivery, and selection- Amazon is almost impossible to beat. Every now and then popular vendors of these kits will have a deal that includes free shipping, when you can take advantage of it, you flat out can't beat the deal unless you're in Japan. So far my favorite seller is 'robot4less'. Although it could be my location, so far they've delivered my kits the very next day 5 orders in a row.
But if you are starting to build a collection and need specific kits to fill it out, you're going to face equal or greater turnaround time when special ordering from a shop. In my experience, it's rare to pay less than $20 in a shop (and the average is more like $25) at minimum for any kit (and rightly so, the store can't be making much money at that price).