How to find the smaller industry players

That's kind of the by design though, you're not meant to find them. They don't want to be found. HF positions at good funds, especially small ones, are typically seats that when a person gets there they want to stay for a while. There aren't a lot of openings, they pay well, there's no normal recruiting cycle, there's low turnover, and as you mentioned they prefer to fly under the radar. For most there's not going to just be an application posted somewhere, and if there is it's probably at specific schools where the PMs have ties to/are top targets. For the ones that don't even post a listing, they'll hire through headhunters who will ignore anyone who reaches out to them. If they want you, they'll find you.

If you're just generalizing about the buy-side, there's so many different types of firms in areas like HF, PE, VC, AM, CD, etc. any will do the same direct recruiting at targets as well as post jobs on LinkedIn, Indeed and headhunt through recruiters. Some will also never post anything and it's the same situation of "they'll find you". You have to do the work to research and figure out what area you want to target, because you have no chance if you just generally say "buy-side" since they all do very different things.