Yes and no.
I know a number of real estate investors who do probate mailings, and most say it's a good source of leads--comparable to absentee owners.
Most of the investors I know go to their local courthouse and do the research themselves. They, like you, haven't found a good source of mailing lists.
Since probate filings are public record, some jurisdictions do post them online. However, the ones I'm familiar with all charge some sort of subscription fee.
Best thing to do would be to go to your county courthouse and ask the employees there about the different ways of accessing the information. If it's not available online, then it's highly unlikely you'd find a third party offering it. In that case, your options would be: (1) research them yourself, (2) hire someone off of Craigslist to do it, or (3) possibly ask one of the researchers you'll find in the courthouse (they often do title searches and other research) what they'd charge.
Another thing to do: Attend your local REIA meetings (if you don't already) and ask some of the experienced investors there if they do probates and, if so, what methods they use.
Finally, many of the investors I know who do probates network with probate attorneys. That way, you get fed leads from the attorneys, rather than having to do all the courthouse research.
Hope that helps.