I looked for the JSON Api at the url you've listed, and haven't found anything. If it's contained in the newest version of buildmaster, we've been holding off on upgrading in case there are any major changes which would disrupt our deploys in process. We're on 184.108.40.206, and I wasn't able to find it in our directories, either.
After we figure out where to get the API from, are there any examples we could use which include and use it in powershell? If not, I've happened upon some examples to use for build a .NET web around it, but we would feel a little more comfortable making a script of some sort. a full web might be overkill.