Hey Western Metal,
Generally what we're looking for is whatever the highest percentage tin alloy is at the lowest possible cost. Most of use use ww for the bulk of our casting which is an inexpensive source of antimonial lead, and it makes the *ideal* casting alloy provided you can bump up the tin content a percent or two to improve mold fill out.
In this regard Lyman #2 and linotype is always in demand at the right price.
To be fairly blunt, casters are thrifty bastards, it's virtually a necessity to get into DIY bullet making.
We scrounge, we've done our homework, and there are plenty of other metal dealers selling alloys suitable for casting (rotometals, metalex, Canada Metals, etc.) that we could buy from but don't because usually shipping is a pain and pricing on small orders isn't favorable.
Anyone who's been at casting for a while usually had hoarded enough lead for their immediate needs so we're not biting at the bit to buy whatever we can at any price-we wait until it's right.
In short, be competitive.
-Mike