I am looking for a provider of a database of worldwide vacation
resorts for use on our website. The database should be comprehensive
and include specific information about each resort (name, location,
ammenities, timeshares offered, etc.)

Ideally the database should be in SQL Server format. I would also
prefer if the provider of this database was able to issue updates to
this database as new resorts are built.

So far I have been unable to locate a company or individual that
offers such a database, though I am able to find numerous companies
(namely our competitors) that obviously are using one on their
website.

Please point me towards companies that offer such a database.

Did you check this one?
http://www.americaslists.com/buscatalog.htm

Yes I've seen them. This site sells lists of contact information for
various industries. We are looking for a database of resort details
(location, number of units, contact information, ammenities offered,
etc...)

You will not find a ready made database of resorts in the format you
require it in. However you can find ample listings of vacation resorts
globally by checking out tons of sites on the internet such as
besthotels.com, resortsandlodges.com, resortsonline.com, etc.