There are a few things you can do. The first is talk to a realtor. That person might have great leads for what you are looking for.
Another option is driving for dollars. Drive around the neighborhoods you are interested in, and look for multi-family homes that appears to need some work. Use public records to find the mailing address for the owner (probably not the address of the property), and send them a letter saying that you are interested in purchasing their property. You will probably have a low response rate, so be prepared to send out lots of letters.
The third option (similar to the second) is to form a relationship with an escrow or title company. See if they can provide you with a list of absentee owners for multi-family properties. In exchange, when you purchase you would do the closing through them. You would then send letters to the people on that list.
@Jorge Quintero have you tried looking for the data on your own instead of using a realtor?
@Account Closed I’ve been driving around and have collected addresses for some properties that look interesting. I plan to get the phone numbers of the owners and call them asking If they’re interested in selling. I’ve also been spending a lot of time on HAR.com looking at listings but those get snatched up quickly and it’s hard to make an offer without having to wait for the realtor to get back to me. Do you have any other ideas?
I'd recommend networking with a few local investors who may be able to connect you with the right kind of realtors and potential pocket listings. Make sure you are pre-approved by a mortgage lender and know the exact criteria you are looking for so you are ready to move. Lastly, target the neighborhoods that fit into your budget so you can narrow your search.