Having checked with as many people as I could, there is no indication that anyone has received or seen evidence that the merchant den mount gear recipes are dropping or being awarded. This makes it impossible to use the patterns we receive from the collections and drops.
There are some mount gear sets: \aITEM -390808436 -2087743926 0 0 0:[Pattern: Merchant's Hackamore of Doublestrike]\/a (from solo collections) \aITEM -1220739976 -999456067 0 0 0:[Pattern: Warewolf Stirrups of Ability]\/a \aITEM 374292479 -1694186613 0 0 0:[Pattern: Glintswift Hackamore of Doublestrike]\/a No idea where the recipies are from. Census of this GU - items is not working so we sadly can not check it
The whole reason for this bug report is that the recipe books haven't been acquired by anyone, at least that I could find.
These were meant to be the actual items themselves, not the patterns for them. (i.e., there are no recipes, there will be no recipes, the patterns will turn into the items themselves.) This should be fixed shortly.