You can discuss general iPXE issues in the iPXE discussion forum. For detailed technical questions, you may also want to try contacting the iPXE developers via e-mail or IRC.
You can contact the iPXE developers by sending e-mail to ipxe-devel@lists.ipxe.org. You can also subscribe to the mailing list, or view the archive of past messages.
To talk to iPXE developers in real time, you can join the #ipxe channel on the Freenode IRC network. If you are unable to use a standard IRC client due to firewall restrictions, then you can try using Freenode's web chat interface.
For commercial enquiries, such as custom development or business-critical support issues, please contact vendor-support@ipxe.org.