SG has a separate SG Auctions site.
Prices realised:
https://auctions.stanleygibbons.com/ArchivesOur auctions >> Previous auctions >>
If you create an account, you can see the hammer prices next to the descriptions after clicking on "View results". Otherwise click on "Prices realised."
The "View results" option tends to have a button "Download catalogue" for a PDF-version of the catalogue. No need to buy it.