While not as frequent as in the Demigod's Quest, Fast Mounts still have a high probability of dropping in the Hunt or Be Hunted raid.
Moreover, since most people already have them, if you declare 'I want a horse,' you can usually get one.
The Hunt or Be Hunted raid is included in the Hunter and Hunted pack, so accounts using the Free Questing Coupon can enter for free.
If I were to farm horseshoes, I would do it in the 'Watch Your Step' quest.
It's a basic strategy for farming with multiple accounts, where after clearing the quest, one person goes outside and keeps the quest window open.
Then, after everyone else exits, the person with the open quest window enters the quest again.
This creates a new instance, so those who exited just need to re-enter.
This method eliminates the need to report quest completion, making farming possible in a short amount of time.
Using an account that doesn't have the quest pack is also an option.
Since it's fine to include a character without the quest pack in your party, you can simply share the quest and leave them idle in the town, allowing you to continuously do quests without having to report completion.