Many ways you can do it. MLS is of course the best source - and checking with other agents and brokers for upcoming investment properties is another.

good question

Research on the MLs, visit the properties and ask, talk to experienced agents in your office.

You have to mention at least your state and be more specific about type of properties you are looking for your client. In general, hypothetically: find the most active agents in your area( it will not be many) and check with them regularly. Or pull all agents who sold that specific kind of property in last 6m-1y. and ask them to add you to their mailing lists. 

MLS is the best.  Depending on your client's criteria it can be challenging to find them.  I have two clients in this space (one being me) and it is challenging to find the right place at the right price.

Call them

Research, research..... check out MLS, talk to other agents and your Broker..figure out whose who in the zoo!

Phone or email

check your mls - do your home work - talk to your broker

Do a detailed search in your mls for specific parameters.

They will be members of your MLS.

MLS and Loopnet, see who is advertising those properties.

I do specific searches in my MLS that use keywords to discover agents selling those type of properties. Maybe that would work for you.

You can discussed it with your broker as well.

Join a real estate networking group.

If you are a licensed agent search local MLS for properties in their price range and preferred areas.  Good luck.  If you are not an agent call local real estate company for assistance.

You show them you have serious buyers they show you their ware.  Most commissions are established on retail sale or bulk.

We can't talk about commission splits anywhere per the DOJ.