Given that Peterson hasn't made one like this in like 80 years, assume that there isn't a pile of old stock stems around. To make one, you are looking at probably 22 or even 25 mm rod stock. There's about 40 bucks in material right there, never mind trying to copy/manufacture the metal spigot. Cutting churchwarden-length stems from stock is a huge pain, tough to drill, tough to shape. If someone really wanted me to make one, it would probably cost a couple hundred bucks. Few people are willing to spend 250 bucks to make a copy of a historical relic.
So that's why there aren't a pile floating around, and it's also why just about every churchwarden you see has the same skinny stem or a subtle variant of it - they are painful to make by hand - much easier to cast a production stem and use that (as STanwell, Savinelli etc do).