It is true that you may have to go there as I have also researched most of the counties there and found that the all of the Counties do not have the Assessment data online.
This is a long shot, but it MAY HELP: If you have the property addresses, goto googlemaps.com and plug in the address and see if there is anything that may help you. Yo may get, at least, a visual in some cases.
Also, just plug in the address on google. If the property was ever listed For Sale, the old listing may still be viewable. If they are vacant lots; however, that were never assigned property addresses, you can only try to find out if a nearby address to determine its' general location and potential land value.
Finally, if you actually attend the Sale in June, let us know how it went, and what you thought of the experience. Some of us may be interested in knowing---at least I would.
Hope this helps you! Much Success As You Invest,