http://www.cabriolet.modelahouse.com/
https://www.flickr.com/groups/114417...7618701086945/
There's a Cabriolet Special Interest Group listed in the sticky notes at the top of the MODEL A discussion section.
Tell us more about your car. What year, color etc. (post a picture)
If your pop out is original and not been messed with it will have the key number on it. You have to remove it from the panel in order to see the #. Depending if it's an early popout or a late popout will determine where the number is stamped. The standards say the early #'s were stamped on the bezel ring and the late ones the # was relocated to the face of the lock cylinder.