I got mine at IKEA! Any kitchen scale will do. They may all do this, I don't know, but mine lets you place a bowl on top of the scale and then re-set the scare to 0, so it just tells you the weight of the snake and you don't have to subtract the weight of the container you set it in. I don't know, I'm pretty easily impressed, but I found that feature to be very novel.

Just make sure that if you weigh prey items to weigh them in a different bowl than you weigh the snake in, because your snake can indeed still smell the rodent after 5 days and will all of the sudden think that the bottom of the bowl is the most fascinating thing it has ever encountered.