Check "oem-parts-from-the-past" on eBay. About 6 weeks ago they got a 64 Belvedere and were selling all the parts from it. I got the fender you were looking for $385 and that included shipping. However, many other parts that you need may still be there.
For the fender on the other side, I ordered a "front fender lower rear repair panel" from AMD. With the part they sent a catalog along. I had no idea they made that many S/M parts for the old Mopars. Supposedly, they're not making any more Mopar parts, but they list a lot of stuff.
