Ismacs article on Sears machines mostly pre manufacturer codes but does describe a few of the coded models:
http://ismacs.net/sears/sears.html
Older article so some info may be outdated but cutting edge in its time.
Joe,
I think the 120 series uses the CC1221, Free Rotary, or Boye 2-1/2 needle. Tough find and $$$. Also called 40F1 or 38Y1. You can also grind 15x1's to size and there's info on the net about doing so if interested. I see some recommend 206x13 as a replacement but there are repeated warnings not to do so. No personal experience with this machine and am just repeating what I read.
Jon