No, I'm afraid you're going to be fabricating something....

Start with trying sheetmetal *tabs* about 1inch long, 1/2 wide. Wrap them around the rack posts. Drill a bolt hole through them, bolt the fender stays into these.

I hope this makes sense...it's easier to do than type directions to!

(make a couple sets of these tabs for future use-- you'll find them handy.)