It sounds too good to be true, but the background work for this is in any law library in the United States. Land patents come from several different places. The original colonies land patents came from the corresponding country of control. The U. S. Government honors those patents because of the treaties. Those patents are still in force as are the patents issued by the U.S. Government today.
All land patents are forever.
The patents that were issued to the colonies can be found in the corresponding state archives. The state senators or representatives seem to be helpful in getting the patents for the colony states. Real-estate brokers can some times get the patents through one of the abstract companies, not only in the colonies but all states. Some states have the patents in the Secretary of States office. For getting the patents in the territory states, the Bureau of Land Management will have them.