This site collates the various archives and manuscripts for sale on popular auction sites. It is not an advertising or auction site.
Contact firstname.lastname@example.org if you spot any good archives for sale!
The lovely people at the National Archives have a tracking service for valuable or significant manuscripts that might be of interest to record offices and museums. You can read more about their work at http://blog.nationalarchives.gov.uk/blog/tracking-market-manuscripts/.
You can contact them at email@example.com