The Lowe's and Home Depot's of the world carry HPS and MH bulbs ranging from 70 to 400 watts.
Something similiar happened to me several days ago...after troubleshooting and determining it was the bulb, and not the ballast...I made a mad dash to Home Depot to get there before they closed....was damned if I was going to let the plants be stuck under anything less what they were accustomed to.
I've had to wait for tomorrow and the end of the holiday weekend before being able to get down to the grow shop and see if they'll be nice enough to replace a 24,000 hour bulb that failed somewhere around 1,000 hours of use.