Why would you want to split the money with the landlords, just mention to them that you do a lot of work for this particular letting agent and you can personally recommend them. That way you get all the credit. Letting agents typically get 10 - 12 % managment fee plus/or one months rent when they let a property.
If you really believe they are good, then recommend them, works on two fronts, one you get commission, two they are more likely to give you more work.