Yes, it is ethical. Biomass is useful, but it is not essential, and Much biomass comes from land or crops that could be used for food. It can be unethical to use something faster than it can be replaced, depending on what it is. To do this with trees is unethical, but with natural gas it is not.
its pretty much everywhere. anything containing carbon is biomass. dirt is biomass. poop is biomass. a tree is biomass. you are biomass. so is your dog.. so, yeah; its pretty easy to get your hands on.