You could buy a broken board which has the featured bracket.
I don't know if these brackets can be bought separately, but whenever I need a similar part for one board, the easiest thing to do is to find a similar part from a donor board and use that one.

Are those brackets alike for all the motherboards?
This is what my motherboard looks like after I removed the water block. I don't know if I would need a new back plate too or if I could use the one that was used with the water block.

Something like this will work. Pay attention to the pattern for the mounting screws. You need a two bolt pattern, not four. It might be smart to pick up a full kit with a backplate. The backplate is less robust, but you have to replace the existing bolts (clearance issues with the spring clip) and this would guarantee a solution if you can't make the old plate fit.
http://www.ebay.ca/itm/NEW-ASUS-AMD-K8-Socket … xoAAOSwq7JT-nLU

After some searching, I found this: http://www.ebay.com/itm/272202539687?_trksid= … K%3AMEBIDX%3AIT
Would that work with my motherboard?

Yes, it looks like a match.

Any 754 or 939 bracket will work.