You can try looking on the web sites of well-known aftermarket cooler manufacturers.
At this stage, you could simply keep in mind to choose a videocard that has a good single-slot stock cooler to go into your SLI setup. The KO line of cards fron EVGA comes to mind.
When you are ready to buy, the market will have changed anyway. Also, many think that it is better to have one very powerful card than two midrange cards in SLI. So if you don't go SLI, you will have a vast choice of aftermarket dual-slot coolers.