Places like NewEgg and up here in Western Canada Memory Express, which cater to the built it yourself, and in the latter's case the gaming community still sell Win 7. I just ordered 3 custom systems from them, had them assemble them for 50$ and install the OS/drivers with every current update included for that price, and each of them have Win 7 installed.
I hear what you're saying regarding the HP and ACER types of "on the shelf" PC's for average Joe, most if not all of the ones I've seen have Win 8. That said, saying Win 8 "works just fine for gaming" is just that..."just fine". I won't bother linking the dozens of articles for and against Win 8 as it pertains to the gaming market. One person of note, Gabe Newell, who runs Valve/Steam stated 'I think Windows 8 is a catastrophe for everyone in the PC gaming space'. I realize this is just one person's opinion, but it's echoed from a lot of others in the gaming community. You don't have to look far for others bashing it.
Myself, I was essentially forced to upgrade my home theater PC to Windows 8. Luckily, the 3 aforementioned systems each came with an upgrade coupon valid until the end of this month to get the 250$ Win 8 pro for 14.95$, so at least I didn't get the good old Microsoft scam price, it was cheap. The reason for this is that my ISP is one of those that is using Netflix's new portal for their "Super HD" content, which streams at 5800 kb/s as opposed to the regular 1700, and while not blu-ray quality, it is noticeably better than 720P broadcast TV level HD. In order to use this service however, if you're using a PC for netflix, you HAVE to use the new Netflix "app" from...you guessed it...the new Windows 8 super duper application store! Which, btw, is NOT available for Windows 7. Yes, you can use a Boxee, or Apple HD TV box, or even a PS3 for "Super HD" from Netflix, but those are really the only other options other than a couple manufacturers smart TV's with wi-fi Netflix capability (I have one of these too, a Samsung 40" 120hz LED). However the point is I WANT to be using my PC for ease of Netflix use and all the other videos I have on it for my theater room with my HD projector, not some crappy alternative. Microsoft and Netflix both are getting a lot of pushback from their users who want a Win 7 solution for this new content, but it isn't going to happen they say. Typical.
As for the OP, which is far flung from this topic I posted on, sorry Ed, if you want any help shoot me a PM. I'm running sli 680's on 3 monitors, and it was a little more finicky to set up than with the 7970 X-fire solution, but the performance is 5/6 and pick em between the two for the games I primarily use, and doing it over would probably = 2 7970 cards or the single 690 card or 6gig 7970 Toxic single card.