I've been making and trying to sell fire pistons for a few years, the sources that Don provided are excellent. A kit is not needed IMHO. No metal parts required, you might want to purchase some quality tender, but there are no parts that you cannot make on a lathe and drill press.
The thing about fire pistons is that they are extremely sensitive. I've never made one that worked more than 20% of the time. If you make one for someone they will bring it back and tell you it doesn't work, guranteed. They take lots of tinkering and patience to get them to work once in a while...and all the while you will be thinking that Bic lighters cost .99