I don't know of any brackets out there to address your specific concern. I'm sure the engineers of these cards take weight on mobos into consideration ad test them thoroughly. Do you move your case around alot? What are you upgrading from?
Upgrading from a GTS 250, the board it is built on is that of a reference 9800GTX+ though, so it's longer than your standard GTS 250.
This card leans a bit, but nothing I worry about. I guess in the worst case I can just somehow build some kind of stand if it leans a lot. I'll just wait and see.
oh and no, I don't move my case around a lot. only once this year have I moved it 50 meters from my desk to the party room across the road in the compound for a LAN party i organized. Might be doing more of those though.
anyways if you come across anything please let me know!
Honestly, i have had some large video cards in my PC and i move it all over the place, the screws in the back of the case should hold it no problem, never once have i heard of an issue with the video card being too heavy for the PCI-E slot, no need to worry at all, unless you're doing pull-ups from it, LOL
^ What he said. The screws will hold the cards in place. If I'm not mistaken the cards are similar in size so you shouldn't have an issue. Even if you decide to move the case around a little more for LAN parties you'll be fine. Just use the screw to hold it down.