First, welcome to the group!
Did Parker ever make 10 ga. hammer guns..... they sure did. If you are new to Parkers, have a look at the "grades" link on the left side of the
www.parkerguns.org main page. There you will find information on the different types and quality grades Parker made. I believe there were 10 ga. made in all the hammer grades. Make sure to click on the "view" button in each section.