I asked in the FrameMaker forum and was told no https://community.adobe.com/t5/framemaker-discussions/extendscript-and-date-formats/m-p/13814769#M79..., but I thought I would ask here as well.
https://www.pdfautomationstation.com/products/item7.cfm - This seems similar to the item above, but it is $99.
https://answers.acrobatusers.com/How-enter-pop-calendar-pdf-form-q19050.aspx - I didn't research all of this options, but it is also talking about PDF Forms.
It seems like it COULD be done, it's bascially just displaying a table in a window with controls to move to different months, and the above could be converted to do that, but I was hoping not to make one from scratch.
All suggestions appreciated!