I have a leaky water main valve (home side) not ball valve. Is it easy to replace and can I get a replacement at a home depot/lowes or do I have to go to a plumbing supply house?

Yes, you can purchase valve at Home Depot and Lowe's. Yes it is easy to replace if you can solder and can turn off water at the street.
Before you do why don't you tell us where the leak is. Is it leaking around the stem, at one of the solder joints or do you mean it won't shut off the water completely?