Small Bear Electronics
https://www.tubedepot.com/products/alpha-16mm-audio-pot-pcb-mount-knurled?fbclid=IwAR0eM9VmOltlKeAf4eV5LKWWNuLdI3NW8orlHVpQwFEiOydZ1O3d24DKBk4
https://www.tubesandmore.com/