Where in retail stores will I find a HPS/MH light?

I can find them, but only in very low wattage. Are there any alternatives like several lights? This is my first grow and I have four plants. I'm not in the flowering phase, or even near it but I'd like to go ahead and be prepared. I cant seem to find a 400 watt HPS/MH light. I can find the bulbs in stores no problem, but I can't seem to find the light fixture itself. I've even asked for help. I'm in the U.S. so if there are stores in other countries that we may not have, don't tell me to go to those. Heh. So is there an alternative, or will I just have to order them off the net?

if you have any hydroponic/horticulture shops nearby, look them up in the phonebook or whatnot. otherwise, off the net.

Thanks I found a shop not too far away that I never knew about.

I dont know of any chain retail stores that carry the ballasts and reflectors. If I were you I would buy it online.