Here's one more little trick:
If there is a "no tresspassing" sign or something similar, there is usually a number to call (in case neighbors see suspicious activity).
Call it. Follow the trail. A good way to get to the decision maker is by having an all cash offer ready at a price you think will be attractive to the lender.
If you are completely stonewalled by that, and don't know where else to turn, look up the REO listing agents and see what AM their listings are coming from. If you can figure out which AM has this property, you can make a pretty good guess which listing agent will get it.
Honestly though, thats a lot of work and I've only done that once for a $2.2 M REO a client was very interested in (it was Jose Canseco's) and we lost out to 4 bids that were FAR over market.
You might be better served putting your time and effort into finding a different deal instead of chasing this one. Or this could be the deal of a lifetime. Just leverage yourself a bit and have a buyers agent do a lot of this work for you.