Bedbug,
Welcome!
You may not be too late for Blue Nord if you try a UK ticket agency. The one that I use is Just a Tickets (I've found them to be very good, though you pay a bit more than going direct, and I've tried to but from the ACO but never found it easy).
Final payment for tickets through Just Tickets is normally December but was delayed this year (new Porsche Centre, computer problems etc) so invoices have only recently been sent out, payment is required in January.
At least some people who pre-booked will reduce their needs or pull out - it happens every year.
There is usually a waiting list, but get on it asap.
Good tickets do become available on the forum, and I've done this myself. It takes a level of trust to turn up on the basis that there will be a bloke that you've never met waiting there on the day with a ticket for you.
If all else fails, just go. You can always find a pitch at Arnage until about Friday.
Watch out. It's very addictive.
Aricus