Does anybody have any Sussex Spaniel puppies for sale? Do not want to buy from a puppy mill.

Contact the relevant breed club in your country (from yur use of the word 'Puppy mill' rather than 'Puppy farm' I take it you are in the USA/Canada).  They will be able to put you in touch with reputqable breeders whose primary involvement in the breed is as a custodian of it for future generations.

In the UK this is a pretty uncommon breed (so I expect it is so the other side of the pond too) so you may well have to wait a good while to get a puppy by going on a good breeders list, but it will be worth the wait.