Before you buy:
Note that Pimsleur program Level 1 in physical media (CD, Cassette) can be bought as a complete package containing the 30 lessons, or smaller packages with just the first 8,10 or 16 lessons.
The 30 lessons package is known as Pimsleur Comprehensive
The 16 lessons package is known as Pimsleur Conversational
The 10 lessons package is know as Pimsleur Basic or Compact
The 8 lessons package is known as Pimsleur Quick & Simple

The digital dowload offers you the possibility to buy packages containig lessons 1-10, 11-20, and 21-30

Pimsleur programs can be bought from  any of the following dealers:

Pimsleur-language.com 
A Pimsleur-Only online store based in USA.

Pimsleur Method
US based Pimsleur Dealer.  Ships worldwide

Pimsleur Italian Downloads
This online store offers you the the possibility to receive your course immediately.  Downloads are not Mac compatible.

Worldlanguage
A 15 years old company based in Los Angeles, California and dedicated to sell languages products.

Pimsleur Italian at Amazon.com
Amazon.com offers all packages of Pimsleur.  Versions are available on CD, Cassette and chips.