The Data Protection Act isn't necessarily about banning the transmission of information; it's also an enabling tool. If the club has registered under the Act, then the club's officials can lawfully use the information for whatever purposes are listed within that registration. It may be that your purpose is covered. (For instance, the registration might refer to 'enabling communication between club members').
If it's not covered, the club secretary should use his discretion. If he knows that what you're trying to post is something that the intended recipient is desperate to receive, then he should use his common sense and provide you with the address. If he's in doubt then he should offer to phone the member to seek his permission to pass on the address.
Alternatively, as MM has suggested, try the Phone Book (or BT's online directory of residential numbers) first or check the electoral roll at your local council office (or possibly at a library).