On the nether hind, if you switch to Rockbox, you'll not only be able to transfer 24-bit 48k ALAC and FLAC files to your Touch but actually play them.
Upsampling wouldn't be the best idea. Instead, you'd buy high resolution files from a vendor known not to upsample and try those out. Unfortunately, most are 88.2 or 96k.
One release I recall fitting your criteria is a DVD (not DVD-A) that contains no visual content but consists of an uncompressed 48/24 recording of the six-hours-long String Quartet No. 2, by Morton Feldman, performed by the Flux Quartet. Target's price is the cheapest I could find just now, though I picked it up for $24 years ago.
This page offers a free 24/48 Rachmaninov recording to test and links to a vendor that offers 24/48. Can't vouch for Pristine Classical's credibility in terms of no upsampling, though, as I haven't had any experience with them yet.
Edited by scrypt - 2/2/12 at 11:42pm