Wheel weights are not "mostly antimony". They are 95% lead and 4% antimony the remainder being tin and arsenic.
Linotype is commercially available from a variety of sources such as
Tin is not the "best" bullet hardening metal. Tin WAS used to harden lead before antimony was available. Tin lowers the surface tension of lead alloy. It allows the alloy to fill the grooves in the bullet mould giving nice sharp edges where they are intended.
Antimony is the #1 bullet hardening metal. Arsenic is valuable also for its hardening qualities.
The basic rule of thumb is adding 2% tin to the alloy increases bullet hardness the same as adding 1% antimony.
I have never heard of aluminum being used in type metal.
A nice primer on the subject can be found at:
Cast bullet reference on lead alloy's, min / max pressure, lube, shrinkage,