It looks like some mirrors have packages going way back (http://ftp.eu.openbsd.org/pub/OpenBSD/), but depending on your use-case, it may be more beneficial to focus on the base system upgrades (documented in the upgrade guide) and worry about the packages later.
That many years of package changes could be troublesome to deal with, and it may be better to fast-forward to whatever the modern tooling would be.
However speaking with my manager I think the long term plan is to dump it for RHEL - too bad because I'd like it on my resume :-) Not every day you can play with OpenBSD in prod - usually it's just on my oddball computers.
That many years of package changes could be troublesome to deal with, and it may be better to fast-forward to whatever the modern tooling would be.