Mapei grout is available from large retailers such as Lowes.com. Home Depot also sells a limited amount of Mapei products, but Lowe's, however, offers a wide variety.
Mapei manufactures both cement and epoxy grouts. The cement grout comes in sanded and unsanded varieties. Each of these is available at Lowe's and is meant for specific uses depending on the location of the application and the material type with which it works best. Lowe's also offers an array of color choices for both types of grout.
Cement grout is generally considered to be easier to work with, while it is difficult to correct any mistakes when working with epoxy grout. Epoxy, on the other hand, is much more stain and chemical-resistant.