In general, we don't, and we couldn't explain why better than this blog post at 37signals, which we recommend reading.
We don't have a list of patches you can just download.
However, we do provide custom patches to PE customers on a case by case basis.
Often such patches are backports of commits publicly available in the public source code repository.
Sometimes, they are created specifically to address issues you report.
Some patches are also available in the latest stable release of Orbeon Forms PE, which you can find from the downloads page.
If you are interested to know what kind of issues and features are being worked on, please make sure to check the following:
No, Orbeon Forms doesn't contact a license server.