you can buy them from ebay, amazon, aliexpress etc. "58mm Embedded Thermal Printer with TTL"
the kits in the lnbits shop have this pcb included to make assembly 100x easier.
Discussion
Nah I meant the USB thingie you put on top.
I thought it was this one but yours looks slightly different.
ah, yes it's this one IIRC https://www.aliexpress.com/item/1005006170575141.html
Wow US$2.50 can't complain I guess