Google does not sell WiFi modems, but they are widely available on the net. Here are links to product information sites for several of the WiFi modems we have worked with in the past:
http://www.pepwave.com/products/surf/
http://www.ruckuswireless.com/products/mediaflex-home-products/mediaflex-2200
http://www.engeniustech.com/datacom/products/details.aspx?id=246
Use your favorite search engine to find outlets that retail these devices.