How far do you want to go ? Only IL or further ?
Just did a google search and found the following :
1984 MacGregor Sailboats 25 SAILBOAT for sale | Winthrop Harbor, IL
Don't forget to check craigslist:
1982 MacGregor 25' Sailboat
A bit further away (they do come on a trailer
25' Macgregor 25' Sailboat Wtrailer 8hp Johnson for sale in Pensacola, FL, United States - 201950 - Boatshop24.com
Or if you want to venture (pardon the pun) into the frozen north:
New & used macgregor 25 sailboats for sale Ontario. Find; masts, charters, catamarans, sails, sunfish, riggs and more on Kijiji.ca
Put some notes into clubhouses in your cruising area. You might well find somebody who's willing to sell without advertising.
And as mentioned, register on the macgregorowners' website. There
are alledgedly over 8000 people registered on there. You'll find a lots of help there.