Alberta Slip is a close physical & chemical substitute for mined-out Albany Slip. It is blended by Plainsman Clays of Medicine Hat. Owing to its relatively high plasticity, recipes calling for more than 40% should introduce the excess amount by calcining it (along with any other clay in the recipe) to prevent excessive shrinkage which can lead to crawling.
For much more information on Alberta Slip including glaze recipes, see the Digitalfire.com Reference Library of ceramic materials.