Marco sells the spring you need. part number: 535-5611-00. Same spring is used on Checkpoint. The same spring is also used on Robocop but for some strange reason Data East changed the part number to 535-5610-00.
NOTE: You just have to know this info about Robocop. Searching for the Robocop part number leads you to nowhere.
https://www.marcospecialties.com/control/keywordsearch?SEARCH_STRING=535-5611-00