I don't remember where I got them, but we were grouping up to take off for the Guinness run and when I got off my trike, the bolt snapped. I weigh 230, and they were less than a year old. I got it fixed with new bolts, but had lost the extension itself. I'm going to work on a new design for some 1.5 inch extensions that are more robust.
I hope you enjoy yours! I know my right leg was a LOT cooler when I had em on.
When I started looking at extensions, I gave thought about how they would hold up with the stress of using the floorboard to get on and off the trike. That's why I bought the extension kit from DK Customs. I found a couple kits that cost less, but I was somewhat concerned about the quality. I am looking forward to a more comfortable ride and less heat on my legs, especially in crosswinds.