JLLebbert is correct. There is very little consistency between what is published on the USPS.COM website versus the USA Philatelic Catalog,
ebay, etc.
In response to your specific question about the $5.60 Verrazano-Narrows Bridge Stamp, you can indeed buy a block of 4 using Order #116302 at $22.40. If you want a single stamp its Order #116351 at $5.60. Both are listed in the latest (2014, Q3) USA Philatelic.
As far as the $5 Waves of Color Stamp is concerned, I had to go way back to the USA Philatelic of Q1, 2014 to find it available in block of 4 format. Order #115720 at $20.00. They are also listed for sale in block of 4 format at the bottom of the link posted below:
http://uspsstamps.com/stamps/waves-colorOne final note: If you are buying the $5.60 stamp for other than collecting purposes, keep in mind that the Priority Mail rate is scheduled to go up to in September 2014 (approval pending) and, if approved, a new stamp at the new rate will soon be replacing the present one (not yet announced):
http://about.usps.com/news/national...pr14_039.htm