The gypsy cobs definitely work, I tested it myself. Try one of these models:
A_C_HORSE_GYPSYCOB_PALOMINOBLAGDON, A_C_HORSE_GYPSYCOB_PIEBALD, A_C_HORSE_GYPSYCOB_SKEWBALD, A_C_HORSE_GYPSYCOB_SPLASHEDBAY, A_C_HORSE_GYPSYCOB_SPLASHEDPIEBALD, A_C_HORSE_GYPSYCOB_WHITEBLAGDON
Also make sure you are on the latest OutfitChanger version in order for them to show!