are you just looking for driftwood that has a similar appearance to manzanita?
Manzanita is a chaparral scrub species, it's pretty common in the California hills. fairly slow-growing, fire adapted.
You can find similar looking wood pieces pretty much anywhere. Lots of people also seem to be able to find manzanita available cheaper (then pet/fish stores) at some florist, craft, and wedding supply places - I guess they are used for table centerpieces and such.
As to finding wood in the wild, if it's not in water, try to find something that's been long dead, and looks like it's weathered several (or more) seasons. You don't want anything with sap or resin in it.