To get the festival horse u will need 3 things: a barter reciept for ur bree-horse (lvl35 horse), 1 all shire race token and 6 festival tokens.
The race token is obtained by winning, the shire race, just S-E of michal delving (near shire homestead).
The festival tokens are aquired by doing fishing quests in bree, thorins and cellondim. U will have to pick up the festival fishing q from the fishing vendor npc east of hobbiton-by-water (the party tree), then go fish at the 3 locations.
The quest itself gives u 3 festival tokens for catching a total of 9 fish - 3 from thorins, 3 from bree and 3 from celondim.........
.......however, u can barter these fish at the quartermaster npc at the party tree for alot more tokens. At the quartermaster the thorins fish is worth 10 tokens, the celondim fish is worth 50 tokens and the bree fish is worth 100 tokens. I believe u have to have the fishing q active to be able to catch the festival fish.
The reciept of purchase is obtained by taking ur lvl35 horse back ti the horse-fields and bartering with the npc there.
once u have these 3 items u can exchange them for a festival horse.
Hope this helps