For the pact broker api, is there any endpoint we can call to get the latest contract version for a pacticipant in a particular environment? e.g. get me the version of pacticipant A in environment dev?

Possibly, you could look at this to see if you can get there: https://smartbear.portal.swaggerhub.com/pactflow/default/getting-started (There is some PF APIs there but hopefully you can see which things are open source vs PactFlow)