US gardeners: are Master Gardeners people that anybody can ask for advice? Is it a paid for service? How do you find your local master gardener?

Similarly extension offices: can just an ordinary citizen ask for growing advice?

We don't have that here in the UK AFAIK so I'm very curious about it.

@Kimberley extension offices are such a great resource! I use mine often. They have often taken a while to get back when I've emailed specific questions but they tend to try and be at a lot of expos and festivals in my area so often I'll try and actually chat in person with them