Ive thought about this idea. You could potentially make an influencer marketplace that brands could search through to find a specific influencer that matches the demographic theyre looking to target.

funny thing is, there are also tons of influencer marketplaces and agencies, it's a space with incredibly low barrier to entry. Thing about the marketplace is, there is little incentive on either side for the influencers or clients not to skip over the marketplace altogether after using it for window shopping

https://fohr.co does this and is probably one of the first to do so (they started in ~2014, I think).

FameBit (https://famebit.com) – acquired by YouTube

Plenty of sites like popsugar already do this.

That was basically one of my good friend’s wife’s job.

I am very loosely acquainted with someone working on exactly this: https://www.joinstatus.com

I’m sure there are others.

Your very late to the game already but it's probably not too late to do something in that area.