Rule 34 isn't strictly hairjob related. "Rule 34" is sort of a blanket rule of the internet, that "if it exists, there's porn of it."

The site rule34.xxx follows this principle, and has millions of posts on there that you can search up by topic, 'hairjob' being one of them. Related ones are 'hair_fetish', 'hair_around_penis', 'penis_in_hair', 'cum_on_hair', and other similar ones. You can also narrow your search down more specifically by adding tags next to your hair fetish tags, like for a specific character, or hair style/color/length, etc. Individual tags are written with an underscore between each word, and you add more than one tag by simply using the space bar between each individual tag.

There's a lot more that goes into it than that, but I think it's worth exploring on your own. Obviously most folks here are gonna prefer real women photos/vids, but for those interested in the hentai side of things, I hope this helps