I keep looking at T2-T6 gear and notice that there really aren't that many items with Improved Block, but too many items with Improved Parry, Dodge, etc. AFAIK, the only common drop that has improved block is the shoulder/back item that drops from a warder in ST.
I can think of several items that are not that rare that can change to Improved Block worn effect. A good candidate would be Ring for the Strong (instead of Improved Parry VII, how about Improved Block VII), Sleeper Ring (instead of Dodge VI, how about Improved Block VI), or Powerful Metal Vambraces (Improved Parry VI to Improved Block VI).