I am probably going to try these:
eBay Motors: 05-06-07 Chrysler 300 300C Drill/Slot Brake Rotors+Pads (item 310039735633 end time May-09-08 00:53:49 PDT)
note the price is for all 4 rotors and 2 sets of pads, just need to sort out shipping.
Other than that, if you just want some pads Zeckhausen Racing are the go. You should be able to get them here for about $100 as set including shipping.
At 55,000 you should just need new pads and maybe a light skim of the rotors, this should cost less than $50 per rotor.
I put EBC Redstuff pads (Ceramic) on the back of my 300C and would not reccomend them to anyone, they squeal a lot, generate lots of dust and look like they are chopping out the rotors fairly quickly. I also got a set of Posiquiet pads from Zeckhausen around the same time and will be using them next time around, you might have to wait a while for the comparison though. The front pads were changed by the dealer at great expense using OEM pads, but do seem to be wearing quite well compared to the original pads.
FWIW: I would suggest going for softer pads rather than harder ones, pads are much cheaper than rotors so you want them to be the bit that wears out quicker.
PS: If you have done pad changes yourself before on other cars, don't be afraid to do the ones on the 300C yourself, it's not that hard. I changed my rear pads myself in less than one hour, the dealer wanted to charge me over $200 to do the same job, they are rip off merchants.