Finding niche hashtags is simply achieved through hashtag-surfing, I do it every day at around 7:00pm, roughly 1 to 2 hours before my post is due to go up. Those of you who want it the most, will do the same. Every day.
I’d recommend limiting the amount of hashtags with over 1m posts to around 2 or 3 per post, the ideal Goldilocks zone would be hashtags with between ~3,000 and ~800,000 posts. You can go lower if the hashtag is to your liking.
Keep doing what you love, even if no one buys it, sponsors it or shares it. It matters that you show up and create.