Has anyone found a good source to download artwork?

I have a found a few sites for one at a time and manual selection but that will take forever. Also, I know the artwork is somewhere on the hard drive that Windows Media Player down loads but after a bunch of research I cannot find where the files are stored. I'm presuming there would be jpegs for each cover.
Online sources say they should be in the folder with the MP3 files, but not.

With only a few hundred, I plan to store the images on hidden pages versus retrieving on the fly which may be a little bit beyond my capability.

Any elightenment is appreciated.