I'll second m. zillch on the sources for true Hi-Res. I own several AIX recordings, they are all excellent, some of the best recordings I own. In my tests they are also excellent in standard CD quality and not distinguishable from the Hi-Res versions. But they are really well recorded and produced, which I firmly believe is the problem to solve anyway, and thus worth their cost.
As to other sites, it seems silly to pay up for a "Hi-Res" version of a low-res recording. Up-sampling doesn't created more audio information, it just creates more data.