SO to answer my own question...

I landed at Milan in March, determined to but some snowchains to avoid the high cost of rental. I knew I would not need to use them and that their purpose was only to avoid a fine if stopped by police (in Aosta).

I tried 3 different supermarkets in Milan - zip. Some signs were up but shelves were empty - perhaps as in March winter supply sales were over ? I found some in a DIY superstore, but not in my tire size. They seemed expensive as well - 50 Euros or so.

With no other choice I rented snowchains, and received a rusty, well-used inferior set of chains. I finally found some chains in a supermarket in Aosta, suitable for a wide range of tire sizes, for about 36 Euros.

D.