I tried buying tickets online, but the southend game is not an option? It says you can buy them online, and upuntil kickoff. But it's not listed as an even in March. Any ideas?
You could try ringing Withdean Stadium? I am not sure the ticket office will still be taking calls. 01273 542100. They may be able to pass you onto someone relevant? Bit of a long shot, but maybe worth a shot..?
I think you would have to arrange a 'collection'. I.e. Handover the dosh when you get there for a pre-arranged ticket.
Can't think of anything else to suggest. There must be an answer eventually as that should go to the main switchboard that deals with the gymnasium etc.