Other considerations:
Getting new people to serve as OMC directors is like getting volunteers for anything. If you can be specific about what you want them to do, they can make an informed decision. For example, ask people to fill an ordinary committee member position, so that they can watch and learn from each of the other roles, and maybe take on that role for a year or two before they rotate off the board?
Have an open forum at the AGM, and have it on the agenda beforehand, seeking proposals to improve the place, and target specific people who come up with good, affordable ideas, to encourage them to try a year on the board.
If you have absolutely nobody ready to take over vacant positions on the board of the OMC, tell the AGM that you are willing to accept proposals to dissolve the company, as it cannot function without new blood. Remind them of the catastrophic financial consequences of dissolving, e.g. reinstatement costs, getting legal and auditor support and advice, loss of value of the dwellings in development, collapse of services such as refuse, cleaning, no management fees collected etc. etc. As Richard Nixon one allegedly said, when you have them by (insert painful image), their minds and hearts soon follow.