Do what I did and find a bolt that goes into the new track rod end and then find a nut that fits that bolt. I have one seized on the car on the adjusting rod so I'll be grinding that one off and fitting new
It's a very coarse thead of 8 tpi and nut inside dia of 0.4" (10.2mm)
Nut size across the flats 21mm
I think that'll be a metric size 12 coarse thread
My local ironmongers. steel merchants didn't stock it and they normally have everything. Metric coarse is pretty useless and just used on wine bottle openers and for gold diggers winding wedding rings on Hugh Hefner when he's asleep etc