I went through the REST API doc of AnthillPro but couldn't find anything useful on fetching source configuration for a workflow.
What I need exactly is the code repository(svn/git) for the workflow. In anthillPro, it can be seen/edited from Administration >> Folder >> Project >> Build >> SourceConfigurations
Have you installed the proper plugin ? Use this site to download what you need - https://developer.ibm.com/urbancode/plugins/anthillpro/
I use AHP 5, so after installing the plugins you should do the followings:
System -> Server -> Plugins
System -> Project support -> Repositories
Administration -> Job -> "Add step icon"
From the steps popup:
Repositories -> source -> GIT -> ALL THE AVAILABLE STEPS
Option 2 (never did that myself) - Add a shell script/ batch as a step and write your own code to fetch you desired code
Enjoy, Eli