I don't think you should have any problem.
For example, here is one:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813138355
But...
What do you want to achieve with a $70 aftermarket cooler for the GTX670?
If you think you can OC it more, then why not just spend that $70 more on a GTX680 in the first place? I know, I know, the GTX680 is hard to find. But that situation will change.
For less than a $70 delta, you can buy a superclocked version of the GTX670.
Graphics card vendors are binning their chips, so there is no guarantee that a stock card will have great OC potential.
Or, for about the same $, just get a GTX690. Crazy.
Actually, the coolers on the stock GTX670 should be adequate. The cards run relatively cool because of the 28nm manufacturing process.
In the end, just how much better than stock GTX670 sli do you really need?