Anyplace that has Veloce 9s cassettes. They are all loose cog, although websites may not specifically point that out.
In the US, sources include (among others):
http://www.hammerpilot.com/
http://www.speedgoat.com/
http://aebike.com/
http://airbomb.com/
Any LBS should also be able to order them through QBP.
Miche Cassettes are also loose cog and are available from
Speedgoat, AEbike, Airbomb and on eBay from Ital Techno. Miche also include a lockring.