Head up to Kienes in Sacramento. They are going out of business and you can probably pick up flies at a discount. They should be able to help you pick flies specific for Putah.

Greg Bonovich use to sell flies, not sure if he still does or not.

Sweeneys in Napa should also be able to help you.

Edit:

I just saw that you are down in San Jose.  I have no idea what fly shops are down that direction.  I haven't fished Putah in almost 6 years but flies for there are probably still primarily small, 16's n down.  With luck somebody else will chime in for you.