Accessing other branches list and artifacts in a build step

I have a build with the Branch specification configured the following way:

+:refs/heads/release-(*)

So, each release-* branch is displayed and can be run as a separate build branch.

In every branch I build a bunch of archives that contain a software product version. The Artifacts paths are configured the following way:

+:*.tgz => release-%teamcity.build.branch%

The problem is that I need to build upgrade archives that require me accessing the following when building a branch:

• The list of branches to determine the previous version branch.
• The build artifacts from the previous version branch.

I was unable to find any information how to obtain the mentioned data inside a build step.

Any advise or guidance would be greatly appreciated.

UPD: solved the problem by using requests to TeamCity REST API inside build steps.