Hi,
If anyone is interested, there are a few VMG8924's on eBay currently. The seller states they've been taken out the box, set up by the ISP then put back in the box as they use they're own gateways. I just paid £40 for one. They're listed as ZyXEL VMG8324/8924 but I've confirmed they are the 8924s.
The seller is: kevinallitt - no affiliation whatsoever, just passing on the information.
Thanks,
Paul