@Matt Nettles I recommend using the county records. It has every property in the county and all you have to do is filter the information if it's in the correct file format. If it's not it could be a little technical. I like to get all of the data and then display it on mapping software to get a birds eye view of all the properties that I want to market to. The best part about it is that everything is free. Unless you have to pay for it at the county level. I've been able to locate commercial land, apartment buildings, Lots, Residential, boats etc... with the owners and property information.
Let me know if you need any help. If it's too technical because it can be with certain data formats. Hope this helps!
@Matt Nettles you should be able to filter 10 units or more by using the advanced settings. They have a filter in there strictly for apartment buildings.