Some of the Major North American Providers do not have their local ranges broken down within registration. It's certainly possible to get a Class D via tracert, however that still does not provide a block range,
Msg#: 4427868 posted 8:10 pm on Mar 11, 2012 (gmt 0)
I get my basic range listings from [iana.org...] which is the official allocation list. Within that list there are various other delegations - ARIN and RIPE at least sometimes allocate outside their regions.