You can check with the Probate Court in the county where your father resided to see if a will was probated. Six years is quite a long time to start taking action, so it may prove more difficult to get the answers you seek. You likely have some right so the best idea is to find a probate attorney who can start working on these issues for you. There could be some serious repercussions for an executor if you were entitled to assets and never informed you.
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If your father's estate was probated, the probate court in the county where he resided or the county where he owned real property will have all the records including the will. Anyone can look at the court files as they are public records.
Even if the will was not probated, the original was required to be filed with the County and would then become a public record. If the original was lost, there are procedures in place where a copy can sometimes be substituted for the original.
Six years ago, any estate over $100,000 should have been probated in court, unless it passed by a non-probate method such as joint tenancy or beneficiary designation.
If there was no valid will, either his spouse, his children, or both would have been entitled to do the probate proceeding and/or to inherit property, and there should have been notice given to all the children if any court proceeding occurred. (Those notices would have at least the court address and case number which could be used to more quickly locate and view the court records.)
Probate court documents are written with much legalese and form language which can be difficult to understand, so a consultation with an attorney is strongly recommended.
If probate was never commenced and there is property such as real estate that you know your father owned, you can check with the county recorder's office to see if and when title was ever changed to someone else.
I have seen many cases where no probate or title change was ever done, and had to be started even ten or more years after a death. If that is the case, you can start the probate proceedings yourself, but priority to be appointed administrator of the estate is given first to the spouse (not ex) and then to the children.
Given the time that has passed and the added complexity this adds to an already complicated legal situation, I would strongly recommend meeting with a probate attorney to go over the situation and review and documents you can gather.