Check here, and go down to the compatibility chart. It's not complete, but it's a start.
You can try other water block manufacturers for a compatibility listing as well, though always look for confirmation. The Gigabyte 7970 OC, for example, had a reference layout in the first revision, but moved to a non-reference layout with the second, despite not changing the product name and model number. Last I checked, EK still had it listed as compatible.
Another option is to go for a universal GPU block along with passive sinks for the RAM and MOSFETs, which means pretty much any card would be compatible. Plus, you get to re-use the block on the next graphics card. The downside is that more heat is dumped into the case from the passive sinks, and they won't do as good a job as a full cover block for VRM temperatures.
In general, Sapphire is the manufacturer most likely to have a reference board design. Obviously not the case for their 6GB model.