A drive down Randall Road between Crystal Lake and Algonquin yields a common site on both sides of the road. Vacant retail spaces. The southern part of McHenry County – much like the numerous shopping centers stretching down the thoroughfare to Batavia – is full of them, and it’s part of Linda Kost’s job to fill many of them. She’s a senior broker and partner at Algonquin-based Realty Metrix.