Duckface, you have no idea how much I agree with you..
OP: buy a service book for the unit you are working on, and read the information on proper tools and their use.... Those auto parts stores you visited should have a Hayes or Chilton repair manual...
12point sockets,,, Sears has lots of them...
3/8 and 1/2,,,,does your question pertain to the socket drive size or the bolt head size?? How your question was presented could have been misunderstood; and resulted in the answers you were given; and again; misunderstood...
Can also help to tell what machine you are working on... One particular socket, such as a thinwall, will fit where others will not....