Where I am, that's easy. Not sure about your MLS.
On our system, you can search for cash sales, or sales without mortgages. That's not perfect, but it will help identify a lot of purchasers who are buying for cash. Many of them will be investors.
Another way is to look at recent home sales and then screen to include only absentee (non-resident) owners. Most people who buy and then aren't living in the property are investors.
Also, get involved with your local real estate investment club(s). Here's a link to some in Nebraska: http://www.creonline.com/ne.html I see two listed for Omaha. You'll find plenty of investors there.
Sometimes you can flush some out by using Craigslist. You'll get a lot of flakes, but investors do peruse Craigslist. Identify a property or two that would be good for investors. Then put it in Craigslist. Don't get all fancy with the listing. Text and a few photos actually will get more attention, since many investors avoid listed properties.
There are lots of other ways, too. But that should be enough to get you started.
Hope that helps.