Kubota BX2200, LS XG3135H, Grasshopper and Yazoo Zturns
Any automotive place should, NAPA etc. Amazon, Ebay, Harbor Freight, etc. If you so need the socket to grip the plug, any deep enough socket will work.
I never thought about it - apparently it's not a common spark plug size. Home Depot sells individual sockets. Get a 7/8" deep well socket, preferably six point. They are available in 1/2" or 3/8" drive. Search Results for 7/8 deep socket at The Home Depot