12x1 might a challenge, mcmaster doesn't list it....and if they don't list it...good luck. He can't make one on that lathe, it doesn't do threading (not technically true...there was a threading attachment, chaser style, but they are not that common).
....but you're in luck....I was able to conjure a 12 year old memory. This guys sell unimat parts: tomstoolstore.com. Fear not, its a tool store, its a stool store. ( like a child I laughed my ass of seeing that name again......anyone remember the snowmobile magazine Sno Track....on the cover it was SNOTRACK, how disgusting.... small things amuse small minds I suppose). I dealt with him once, good guy. He's got the part for $18 US
www.tomstoolstore.com