this happened to me ..if they are nissan locking wheel nuts you should be able to get replacements because most main dealers carry master sets... and can get replacements double quick..
hope this helps
I have always had success with using a larger socket and bashing it into place over the nut. It should have enough grip to let you undo it.
However, on my brother's car there was one nut that simply would not come off. He drove down to the local tyre place and they just bashed a very industrial looking socket over the top and then off it came. They wouldn't take any money for it either.
if the nuts on your wheels are in steel made.....
you can take a steel axle 12mm or a 12mm bolt too weld them on the key nut head but please do use a electricoweld only .
then turn of with a big plier or a wrench if you weldet a bolt on the key head .
work is done without any damage but the welder should be tremble free
Have you got a pic of the actual nut (not they key)? I'm pretty sure most MOT stations, garages, tyre shops have the facilities to remove them... I had a set removed in under 30 mins local to me, for £5 a nut.