If you have the OEM lights, you can still get replacements at NAPA. They seem to have the best prices(Less than 3 bucks with bulbs) and they are usally just in a bin. Be sure to get the gaskets too. The biggest difference is that your originals may only have one bulb and the new ones will have two. It uses more current but brighter is better in my book.
I would also reccomend getting some new stainless screws to attach them as the old screws may be pretty rusty. When I have replaced lights I always cut the wire as close to the old fixure as possible. Prior to crimping on a new one I also use an anti-oxidant on the new and old bare wire. There is room between the light and the gasket for the extra wire.
It takes 10 min. per light but boy what a diffrence!
BTW if any of the old lenses are still ok save one of each, as you never know when you may be on the road and need one.
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato