steve- i didn't think of the tuskers because they are constructed differently in that the outer laminations don't extend to the tip like that of the zwickey, magnus style.
as far as i'm aware the Kayuga old school heads have a 5/16" ferrule. they have limited weights and sizes also.
i cut my teeth on black stumps and still have a dozen originals. i don't even know if you can still get them. heard they are now made in china and have had quality issues. their website seems archaic.
never had good luck with outbacks either. bent the first one i ever shot in a phone book. then a couple of years ago i broke some while sharpening on my jewel stick. snapped like glass. turned out to be a bad batch of heat treatment.
the options for glue on heads in Australia is limited to say the least.
i'm currently running a mix of magnus 1 (no longer made), blackstumps, grizzly and simmons treesharks.