I recently acquired an older Shure microphone that I can't seem to find any information for. The model# is CR10K. I can't find any mention of it anywhere on the 'net nor on your site. Is it rare
Your CR10K is a the Shure model 510, also known as the Hercules. It appears in the Shure 1949 catalog and was priced at $12.95.
It is not a rare model and was often packaged along with a tape recorder. Your model number CR10K was likely requested by a tape recorder manufacturer, and Shure obliged if they ordered a large quantity.