Coleman has them.
The more important question is which spa has neck jets that will target your neck. Dry test, wet test.
Although I no longer sell D-1, I do feel that the neckflex system offers some the strongest and most adjustable neck massage.
Tubs like Coleman and Master offer neck "collars". Most Coleman models have this feature in two seats, one deeper than the other other. "His & Hers" if you will.