Menards, Lowe's and The Home Depot all sell suspended grid ceilings. The suspension grids are available in different materials and sizes to accommodate a variety of ceiling tile inserts. Some stores have individual grid pieces available, while others have complete kits as well.
Menards and The Home Depot have polyvinyl chloride components for the HG-Grid system available. The PVC pieces work for constructing 2-foot by 2-foot or 2-foot by 4-foot panel grids and are easy to cut into custom dimensions. Lowe's stocks the galvanized steel grid system by Armstrong. The home improvement store has a wide selection of ceiling tile styles from Armstrong available as well.