I'm in the same boat as you, this is what I do:
-Drive and find specific deals that look attractive to me (deferred maintenance, can tell owner isn't present etc). You can also hop on Apartments.com or just Google 'Apartments in whatever city' and find ones with bad reviews or ones that just look bad.
-You can find the tax information online and see who the owner is. If it's under an LLC you can also find the LLC owner.
-I send them a hand written letter first. I know this isn't efficient but, again, I'm sending these letters to specific owners so it isn't like I am sending 300 a week. People seem to really like the hand written letter. It basically just says who I am, I like the property, and would be interested in chatting about purchasing.
-I had professional post cards made that pretty much sum up what I said in the letter. I added a nice apartment picture to it and of course my face is on there (and a stack of cash, enticing, I know!!)
After about two weeks of the original letter sent, I'll send them the post card. Then they will get the same post card again 2 weeks later. Now at this point they know who I am, so the postcard I'm creating now is a little more personable.
Have already had some responses with this process. Just need to keep yourself top of mind to them, that is why I am hitting them twice a month.
Best of luck!!