@Paul Gay Congratulations on having the ambition to work towards you masters AND study real estate!
A big part of the direct mail is your target audience. Finding off-market leads is a numbers game. It's also a delicate balance; reaching out to enough people so you have a chance - but also limiting your list to people likely to want to sell.
There are some do-it-yourself sites like ListSource and ListAbility, but you might consider working with a list broker. A broker has access to quite a few different lists and can make recommendations for your market. And the good news is that many brokers have similar pricing to the on-line sites.
The following are some considerations:
Absentee Owners with Equity (be aware that in some markets that these guys are getting inundated with mail)
Seniors with Long-Time Ownership (ready to downsize or transition to assistance)
Owners with Low Financial Stability Scores (ready to cash out and have deferred maintenance and updates. You have good opportunity to make better profit)