I have had dealing with both Barry Neuhard and Stonemills and have had good experiences with both in regards to Durst parts and manuals. I use both a Durst 138S and an AC800 and have stockpiled some extra parts and manuals because of parts starting to become harder to find.

http://www.neuhardassociates.com/
http://www.stonemills.net/inventory.html

Gord