I'd like to be able to password protect certain tickets with an access code, so that only buyers who have been given the access code by us could purchase.

For example, I ran into an problem this year where we sold out of our capacity for an event, but a number of speakers hadn't registered yet so we saved tickets for them. In order to get them registered, I had to add back available inventory and ask them to promptly purchase their ticket, which is sketchy since technically that inventory is public and anyone could've happened upon the site at the right time and snagged their ticket.