Does anyone sell them
Assuming you’re referring to beer engines that are used to serve beer from casks. Not sure what’s available here in the US, but they are available in the UK. If you contact Porter Brewing in Redmond, Oregon, I’m sure they’d tell you where they purchased theirs. I know it was from the UK.
Or you can make one from a corny keg… https://www.youtube.com/watch?v=ea3ZeUoQGEo