Joe,
Just about all available Hong Kong pop SACDs are listed at
sa-cd.net. Just click on "Titles", then select "Chinese Pop" in Genre, hit "Go", and you will see all of them listed. Unfortunately for my wallet, I own almost all of them (and upload scans of covers and information to Stephen, the owner of the site).
Regarding Sam Hui, I am a huge fan. He has 3 SACD titles issued. The first 2 are compilations. However, they are mostly his ballads from his Polygram years (1974-1983) and almost none of his rock/uptempo songs. The songs from his Cinepoly years (1985-1989) are completely ignored. Given the age of the recordings, the sound quality is very good. The third, and latest, Sam Hui SACD is the soundtrack to "Private Eyes".

You probably already know that every song on this album was a hit and this is perhaps
THE landmark album in Cantopop. Highly recommended! I have the 18 CD boxset and it's really nothing special in terms of sound quality. Yes, highly collectible since only 1,000 are available (I have #547, I think), but no sonic wonder. If you're looking for a good Sam Hui compilation, there's a DSD-remastered 2 CD compilation called "Sam Hui Champion Hits" from Universal Music of Malaysia. It's a legit item and the sound quality is excellent; packaging is much better than the 18 CD boxset as well. You can order it
here.
For Teresa Teng, Hong Kong Universal Music also issued 2 compilation SACDs. I highly recommend these but they are going out-of-print. Sound quality, like the Sam Hui releases, is pretty good given the age of the recordings. Just one Teresa Teng album has made it to SACD, but it's her masterpiece "Dann Dann Iuo Chyng" (this was printed on the inside ring of the SACD).

There's an ongoing argument whether which version sounds better....the original CD from the 80s, SACD, XRCD, HK vinyl, Taiwanese vinyl, etc... You can catch the action
here. The original master tapes to most 70s and 80s HK Polygram/Philips recordings were probably lost during the big fire at its Dragon Studio several years back. The sources for the SACDs were probably back-up copies of the master tapes.
As for music from TVB martial arts dramas, there's a SACD compilation from Crown Records. But most of the songs are from the 70s. Who's Louis Cha?
As for where you can get these SACDs,
malmusic.com is currently have a sale on the HK Universal SACD titles. As much as US$8.00 cheaper than yesasia.com per title (malmusic's price are in Canadian $$, but it does give you the exchange value for US $$ when you click on a specific title). You can also find other HK pop SACDs there, including the now out-of-print HK Warner Music SACDs. Even in San Francisco Bay Area, where I live, there's exactly one store that sells HK pop SACDs.
BTW, all above-mentioned SACD are stereo hybrids.
Edit: OK, finally figured out who's Louis Cha. So you mean music from "The Legend of Condor Hero", "The Swordsman", etc...? Actually, these songs are available on SACD, but they are spreaded out on various SACD compilations from HK Universal, HK EMI, Wing Hang Records, and various singers. Malmusic.com has all of them (Disclaimer: I don't have any association with malmusic.com, other than being a customer).
Edit #2: Looks like Hong Kong Universal has just, as in today, reissued Teresa Teng's "Dann Dann Iuo Chyng" on yet another hi-rez format....vinyl record!!