Buyside Retained Search - Success Based Fee

Hi all, I’m getting close to wanting to hire a firm on the buyside as I’m ~6 months into my search and want some additional eyes, ears on my team.

Has anyone come across a firm that will do it on a success basis vs upfront fee? I’d rather not part with my funds to these unknown entities upfront but haven’t come across anyone in this segment of the market willing to do it yet.

Thanks