The alpha port was derived from the NetBSD/alpha port. The main difference is that the OpenBSD port is self-hosting, i.e. all the tools needed to build a full system is included in the tree. Currently Niklas Hallqvist <niklas@openbsd.org> is maintaining the port.
Thomas Graichen <graichen@openbsd.org> creates OpenBSD/alpha snapshots from time to time. You may find them on the usual OpenBSD ftp servers.