Trade-me is a good place sell vintage computer items. However, you might want to sell (or give away) something to a fellow vintage computer enthusiast rather than a second-hand trader who will just bounce it on.
If you've got a vintage item you want to dispose of, why not post a note here. You never know who might be browsing.
If it's eventually bought or claimed by someone, just post a follow-up note to let people know you no longer have it.