I get mine at The Super Media Store. If a disc is a 52X disc it should have no problem burning at a slower speed.
My recorder is a Marantz CDR500, a Pro recorder. As per Marantz today, they advise me not to use anything higher than 32X speed, with recommended discs being TDK, Sony, Fuji, and Taiyo Yuden. My machine records at 2X in the fast speed, if you can believe that. I've tried Mitsui (MAM-A) 1X-16X, but most will not initialize. TDK and Sony music discs are no problem, but I would like to use a better disc.
I get mine from cddimensions.com. Prices are competitive and service is good. They also sell an extensive line professional CD equipment.
If you haven't seen it, check out the Taiyo Yuden water resistant ink-jet printable CDRs. They have a gloss finish and turn out an absolutely stunning label. You'll need an ink jet printer that can print directly on a CD, but Epson has printers that start under $100 (the R280) that will print on a CD.
The disc will only burn as fast as the drive. So there should be no problems using a disc with higher specs than required.
Just in case any Canadians are reading this thread, here is a reliable Canadian source:
Taiyo Yuden used to make them for Fuji and some for TDK and Maxaell as different brands contract alot of this out to a number of Disc manufactors.
Go to a store that has a few different brands and look for the ones that are made in Japan. You have a very good chance of them being Taiyo Yuden if the label says made in Japan. I have software that will tell me info on the disc as to who made them. Most are made in Taiwan