I procured a 4plex last year.

It might be too late to find a buyer's broker for this property, as the seller's agent may refuse to pay commission to the other agent based on who is the "procuring cause" of this particular sale.However, it's important to remember that the seller's agent is a fiduciary to the SELLER.  

Where is a good place to procure this kind of lease? 

Hire them to procure the tenant for you. 

Currently I own two buy and hold properties in Mass but am looking to take full advantage of my three licenses and possibly help out of staters procure property.

That means that 8 hours or 2/3rd of your day needs to be spent on Lead Generation and Procuring New Clients.

If you are not performing Lead Generation and Procuring New Clients on a daily basis you will NOT be a successful Real Estate Agent.

@Austin Jacob wood what that means is that the Commercial bank that you go ahead and procure financing through would hold for example 70% and the seller would hold 15% meaning you would need to bring 15% to closing.Its easy to understand BUT its not always possible because the lender may not allow it.

Assuming I'm able to procure my brother's share, is $300k netting +6% each year a worthwhile investment relative to having it in the market with more liquidity and potentially higher returns?

I’m looking for an investor friendly real estate agent familiar with duplex and procurement of land in the Glendale area.