Cromwell - Kit available
Russian
T34 - WSN RTR
IS2 - Kit Available
KV 85 - Kit Available
American
T95 - obscure and expensive! can be made from Tamiya Sherman parts and styrene sheet.
Jackson - Turret kit available, hull hopefully soon
German
Panzer VI J - cut a couple of return rollers off and ask
http://www.panzerparts.com/ for their late model mantlet and gun.
Stug 4 - Asiatam
Panzer IV 70 A or V - Profiline for the Alket version and Modellio for the V/70
ROF pak 40 mount - 21st Cent for 1/18, look for papercraft if you want 1/16 scale
Hetzer - bluestar model co.
I never cease to be amazed at these "Why don't they make the most obscure tanks in history?" threads - the bottom line is that if Tamiya or HL don't sell 10,000 units they aren't going to make it - I defy anyone here to find 10,000 people who have heard of a Comet, or any of those paper panzers you all so much adore...