While the Eau Claire Walters Brewing and the Appleton Geo Walters put their beer in cans (the Menasha - Walter's Bros did not), I don't consider any of the cans produced by them to be terribly rare or hard to acquire.

Walter's in Eau Claire did produce a cone top and a couple of flat top beer cans.  Appleton Geo Walter's produced flat tops and pull tops.

Eau Claire produced quite a few pull tab cans for some contract brewing as a means to stay afloat.