the only bike store in Hayward is Cyclepath, unless you're talking about nearby Castro Valley, Eden Bikes who carry Orbea (Robin Williams got his there!). There are two bike stores in Castro Valley, I forget the name of the other one (because I don't like the service as well). Neither are my LBS, which is Robinson Wheelworks, San Leandro. Although different towns all are within a couple of miles of each other.

Cyclepath and Eden both have websites so easy to ask about the helmet.