Deere would have them but Ag Express or others may be cheaper. 

I have made my own connector on a 7830 by teeing in under the right hand console display.  I didn't like the way that the large connector sticks out of the cornerpost.  On this 7830 at least, there is a cable marked Radar under the display and I just made a tee to insert in that spot and lead out along the right window into the cab area.

I put a Conxall connector on this wire for use with a Raven 440 but an Amp connector could be used to connect to the 250 planter monitor.