You can have a look around the woods.....just look for hard woods that have been dead a while. If you can easily leave a fingernail impression it is probably too soft. Avoid sappy woods like pine. Only problem may be weather or not you can get it to sink.
Online I have heard of people buying manzanita from bloomsandbranches and saveoncrafts.
I got a nice box of manzanita off of the for sale forum here for $45 that would be perfect for the look you're going for.