Check out this web site: www.puertovallarta.net A very detailed map section.
Most of the shopping is by the River Cuale (New Town) and on the South side of the river is Old Town also know as the Romantic Zone. Great shops in old town and not so crowded like in new town.
Also there are vendors on a chunk of land located on the river is what is called Isla Cuale, a boutique market called Cuale Island Market that operates every day. It is between New and Old town, a few blocks up from the beach.
Hope this helps you out.