Well I know of two in Kent. Michael Vine of Kent Gypsy Horses based at Paddock Wood, and Albert and Amy Coates of Coates Gypsy Horses who are based Dartford way.
Are you looking to buy or send a mare to be covered?
If looking further north, Emma and Richard Green at Higherveiw Farm, Barnoldswick, have some lovely cobs, including the stallion Apollo II, who was highest placed Trad at HOYS several years running. My boy Eric is one of theirs and is an abolute star1(Though I am biassed, I guess!!!)