If we assume that all of those books get added with a store identifier, for example, all Amazon books I import are saved with the mobi-asin identifier, then try this as the value of a custom column of type=column built from other columns:
Code:
{identifiers:identifier_in_list(mobi-asin,Amazon,)}
{identifiers:identifier_in_list(sonybookid,Sony,)}
{identifiers:identifier_in_list(barnesandnoble,Barnes & Noble,)}
{identifiers:identifier_in_list(google,Google,)}
Add an extra line for whatever identifiers match up to whatever sources you have.
Google ids are "google" and amazon books are imported with "mobi-asin", but I made up the barnesandnoble identifier, since I have no idea what it actually is they use as an identifier, and sonybookid I found on a mobileread thread, so it *should* be valid.
This will add multiple references if you have multiple specified ids that match.
General syntax:
Code:
{identifiers:identifier_in_list(identifier_name,text_to_display,)}
where text_to_display is what will appear in the custom column.
If you download metadata you may find, for example, the google identifier being added which may throw off your column, be careful and make sure you know what id's you are testing for and when they may be added.