You'll find the link on the left hand side of the horse's page, below all the stats

It doesn't matter what tack you put on the horse, so long as it's all 100%.
Also keep in mind that what discipline your horse is. For instance, Halter horses only need a bridle and whip. And people often freak out why they can't put a saddle on their newly trained eventer, only to discover that they forgot to change the disciplines
