Unfortunately the long hair fetish scene on reddit is rather niche.

There are a decent amount of long hair subs, but they're not the most popular and don't see a ton of posts.

The biggest one, r/hairfetish, is MUCH more skewed toward hair cutting.

Some specific long hair ones I know of are r/Rapunzel, r/longhairgoddesses, and r/hairjob. Also r/HairArt and r/AnimeHairjob if you're into hentai/drawn hair porn.

Also worth mentioning r/CumInHair. It isn't strictly dedicated to long hair, but there are some great posts on there.

Hope this helps!