I'm not aware of a retail 10.6.6. A "final" retail 10.6.8 release would have been awesome.
Oh, indeed it would have been! The availability of such a release would have made reinstalling Snow Leopard onto my C2D MBA so much easier as it requires at least 10.6.4 - which had never received a commercial release.
So in short, I would like to get a hold of that 10.6.7 OEM as an image. I know Archive has it, so I’ll be heading there for that.
I downloaded a copy of 10.6.7 via this post and modified it using this guide to replace the installer package with one from the 10.6.3 retail disc and I was then able to create a USB installer for the MBA. Be warned though that you'll need to use an older macOS version than El Capitan because I ran into problems attempting to use it to carry out the modifications. In my case, switching to Snow Leopard resolved this issue.