StayOnline will make you any length extension cord you want if they don't have it in the desired length pre-molded, but it will cost more that way. In fact, it appears that all their 14-50 extension cords are very expensive (in the ~$175 ballpark for a 6ft cord!).
It would be a LOT cheaper to buy a 6ft pre-molded 14-50 appliance cord and a 14-50 receptacle - looking on eBay you could build your own for less than $50.
You also might try John at
evseadapters.com. All the adapters on his site are geared around the Nissan LEAF
evseupgrade (L6-20R instead of the NEMA 14-50R that Tesla owners need), but he can build you anything you want and would probably cost about the same as doing it yourself. Maybe he'll start offering 14-50 adapters by default on his website. (I have no affiliation with evseadapters or evseupgrade but am a satisfied customer of both).