I've been looking for a metal halides for my customers but I can't get wholesaler prices, the prices that I got where worst than the retail price in marine depot... ???
If you want retro kits, they are pretty simple and cheap to build using UL ballasts from an electrical supply company, a reflector (fabricated or bought), and wires are cheap. The most expensive piece is going to be the bulb. Bulbs can be gotten by a lot of wholesalers if you buy bulk to save $$.
If you have a retail storefront you should be able to get wholesale pricing from Hamilton, Champion and others. As Glenn said there's not much money in it buying in small volume but it's a good convenience for your clients.