I'm a long time lurker on this forum but it's my first post here so please be gentle!

As a surprise for my other half I'm looking to rent a Chevrolet Camaro for a few days at the start of our wedding/honeymoon trip to California in a few weeks. I've booked rentals for other parts of our trip through avis.co.uk as I have an AWD number from my employer that gives a decent discount but the Camaro is only available for bookings through avis.com, and that site doesn't give any discount for my AWD. I'm looking for an alternative but not coming up with much, possibly because it's one of their "cool cars" or because I'm a UK resident rather than US?

Details of the rentals and AWD codes tried so far (none of which have any effect on the price) are as follows:

Location: Pick up & return from/to SFO
Dates: Sat 18 Sep 2010 @ 10am to Tue Sept @ 5pm (4 rental days)
Standard price with no AWD: 266.40 UKL (I assume that's £)
Includes LDW & ALI, unlimited mileage

A074800
A108300
A177232
D454000
B790073
K019300
K817625
K860600
U606753
D900888
K817700
W0911098
W2091198
U704363
K816401
B136099
K444404
TUWA058
G417900
A113400
A972200
A686200
X602000
Z652297
L358190

Oddly I'm 99% sure I tried G417900 earlier today as it's saved in my previous Google search results (was trying to find a bit more info on using this code) and it came up cheaper but excluding LDW and with some other restrictions - now it doesn't seem to work for me at all, and when the price results come up I see that the reservation shows AWD N/A instead of a code. Am I doing something wrong here? Should I just give up on trying to get this any cheaper or is there anything else I could try?

Any help would be much appreciated.