They should have it online and free.. http://gunmanuals.net/
You must have a Western Field Model 72C lever action rifle, which is a Mossberg 472C. Try gunpartscorp.com or eBay for an owner's manual. A repair manual is going to be tough as the gun is not well known.
Try contacting the maker.
depending on the rifle i would check ebay. or just google it.
Want ad, for sale ad, on line auctions, gun shows, gun shops, pawn shops, estate sales, garage sales.
No known web site.
what type of scope mounts do I need
See the link below for the Owners Manual.
If you are looking for the owners manual go to the Crosman home page and click on "download a manual" you will find the 500 owners manual there.