Some ideas:
1) Have you tried chatting to neighbours? Surely they must know who the owners are and be able to provide some clues on how to contact them. It might pay off to spend a day knocking on the doors of the neighbourhood and maybe prodding about in the local bars (which is where much of the local gossip is to be had, and you may soon learn the life story of the present owner).
2) If you think the house will go for more at the auction, why do you think the owner would be prepared to sell it to you for less?
3) Have you fully considered that if the house is emabrgoed for that much, that the owner was probably in serious financial difficulties, and that may point to other problems such as seriously deferred maintenance, unpaid bills etc. Is the house really so special that you want to take that risk?
4) In my own experience, another way to go is to talk to a local lawyer. they have access to files in the ayuntamiento that you as a lay person cannot get. It may cost you a little, but if it gets things done, that may be wirth it.