If you could deliver on all of those things, I would be willing to pay 10%-20% of my annual salary for it.

However, much like executive search, this is the kind of service that would need to essentially pay for itself.

E.g. If I could get a $100K salary on my own, I would expect you to find me similar positions for $120K to justify taking a 10% finders fee from me and not from the company.

Also this would need to have contingencies built in for a poor fit. A minimum 3 month tenure with a prorated amount payable over the remaining 9 months would probably be enough for me.