Oilman,
You asked about the initial caliber offerings. Warren Center conceived the Contender as a lightweight, small caliber hunting pistol, so it was originally chambered in fairly light calibers. There were five initially. They included the .22 LR, .22 Mag, .22 Jet, and two others that have escaped my feeble brain. I'm fairly sure one was the .38 Special. Maybe one was .22 Hornet. I know that before 9 months of manufacture the .256 Win Mag was being offered. The original grip design made large calibers PAINFUL.
Hope this, along with the info Graybeard has supplied, helps get you started.
RonF