Finding a list of Apartments that have sold to determine value?

[David Gonzalez]

Hello BPer's!

I am a Real Estate Agent who would like to start brokering the Buying & Selling of Multi-Family homes (2+ units) as well as one day buy them for my self as an investment. Before I would even think about brokering these deals (or investing) I would like to determine what Multi-Family homes are currently selling for. 

My goal is to get a list of Sold (& Currently Listed) Multi-Family Homes in my area so I can start seeing what prices are currently like in my market and serve as a starting point to really understand the value of Multi-Family homes by analyzing deals. As of today (6/9/2016) my MLS shows a total of 47 listings. This is for a county that has over 800k people! I feel that much of the activity is probably happening off the MLS.

Question:

1. How do you find properties listed outside of the MLS?
2. How do you find a list of properties sold outside of the MLS?