IDF's are essentially a shorter version of the IDA. The IDA has been renowed with top level racing since the 50's [F1 to club level]. IDF's are a good option especially when bonnet clearance is to be considered.

The DCNF's are typically thin on the ground as they were fitted to the classy Italian sports cars such as the Maserati V6, Fiat Ferarri Dino V6 [40DCNF]. These carbs can demand very high prices. Not to say that a bargin cant be found.

The carbs mentioned above are usually sort after by the VW beetle people into racing and hot street motors. try VW forums

here is a listing I found on fleebay.
40 DCNF weber's