You can typically find ethernet cables at electronics retailers, office supply stores, and major big-box retailers. Depending on your current location, several national chains and local specialized shops likely have them in stock today. Electronics & Computer Specialists
Convenient if you are already out running errands, though the selection may be more limited to common lengths (5ft to 50ft). Department store ClosedPhoenix, AZ
: A reliable option for standard lengths. You can check local availability and buy online for pickup at Best Buy .
: Often cited by users for having a massive selection of networking equipment and competitive pricing.