I've read to change them 6-12 months if they are used one grow after another. Perhaps others can verify that?

I am sure that yes you can get one at Home Dept, OR you could get two shipped to your door for about the same price. Go to 1000bulbs.com and they even have thinner bulbs to fit in a tube/hood better.

Are their PlusRite bulbs good??? The 400W HPS is only about $7 and the specs are there. One from Home Depot is what, almost $30?