Every festival here needs to be asked about specifically. The area, the festival and the date are all different from one place to the next, and many of them move from year to year. There is no national calendar you can plan against. The dates come from the people who live there, and the way to get them is to ask someone local.
Why there is no list on this page
A page like this usually comes with a tidy table: festival, month, place to see it. I could write one. It would be wrong, and it would be wrong in the way that costs you a trip — because the festivals out here are not organised regionally, they are organised locally.
Two valleys an hour apart can hold the same kind of gathering on different dates, or hold it in a way that looks nothing alike. One of them happens and the other doesn't this year. A fixed calendar written from a desk is a promise the ground does not keep.
How to actually find out
Ask, as close to the date as you can, from someone who is there. That means the guesthouse you are staying in, the driver, the family you are eating with — people whose information is a week old rather than a year old. This is a large part of what knowing people locally is worth, and it is why a trip planned with someone on the ground looks different from one planned from a search result.
If a festival matters to your trip, build the itinerary so you can move: keep a day loose, and be ready for the answer to be "that's next week" rather than "that's today".
What festivals are like when you do find one
They are local events rather than performances. People are there because it is their festival, not because there is an audience, and the most interesting parts of the day are often the ordinary ones around the edges. Bring the same courtesy you would to someone else's family occasion: ask before photographing, don't get in the way of what is happening, and don't treat arriving as an entitlement.
Questions I get on this one
When is the horse festival?
Can I plan a whole trip around a festival?
Where do I find the dates?
Do I need permission to attend?
Written from being on the ground here rather than from a guidebook. Related: when to come · photographing people · all essentials