question re aluminium grade

i have a set of plans from an old popular mechanics mag for building a gem faceting machine . in the plans a lot of the components it says to machine or make from "hard aluminum " question is in todays world what would i use for hard aluminum to make these parts from . and to push my luck even further any idea where i could buy it from in toowoomba in small amount as in not a full length .of course the plans are imperial just to make it a bit harder . so 3"x 1" is not going to be that it will be 75 x 25 i should think .
johno


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