I can't say for sure but you might want to try to contact Julius Blum, Inc. and e-mail them or call them to see if they can help you. They do make cabinet hinges and drawer rails and they MAY make safety hinges. While you're at it, I'd like to pass onto you a couple of items that the US Consumer Product Safety Commission (CPSC) suggests when providing a toy box for a child. These are also supported recommendations by the Toy Manufacturer's Association too.
1) A toy box should have spring-loaded safety hinges. 2) It should have at least a 3/4" cut-out on the top of the front panel to prevent little fingers from getting accidentally crushed. 3) You should drill air holes into the toy box. 4) A toy box should not have a locking mechanism installed.
I know you (and your son) may not want to hear that you will have to partially destroy a family airloom to make it safe. The best choice, in my mind, is to put this box in a safe place with the lid removed, and build (or buy) a toy box that's already safe. Airlooms like this are nice in their original condition. At worst, take the hinges off your toy box and have it function just as a straight lid. You can set the lid under the box or behind it so it's out of the way of the child. I guess I'd like to preserve this family airloom. A safe toy box is easy to build (and inexpensive if you will buy one), and this can become a NEW family airloom! I'm just a stickler for preserving history especially if it's directly a part of my life, such as a toy box. :)
Just something to think about. Best to ya and hope this helps in more ways than you originally thought.
PS. My oldest sister is using our family toy box to store blankets in. As I described, the hinges were removed and are in the bottom of the box under the blankets. She bought a small pad to put on top and is using it to double as a bench to sit on when she and her husband put their shoes on.