001 405 954 3261 is the phone number to call to get through to the FAA Airman Certification Branch in Oklahoma City.
Ask for a Fax of your details, and tell them that you have to fly an N-reg in the UK or something and you should be able to talk them into send you a temporary authorization lasting 60 days.
Ultimately you will have to splash out with $2 to get a hard copy.
Peter
I think Oklahoma is 5 or 6 hours behind UK time. This office will close at 3:30pm CST