urgently need help re foldable tyre

Well with one week to go and living in the sticks I am chasing a foldable
tyre (simply because it is easier to pack in the panniers). I am starting my
tour with 2 700c x 38 not quite slicks and want to carry an extra tyre "just
in case". We will be doing 350kms on dirt tracks towards the end of our trip
and because I do go on dirt roads for quite a few of our trips I am thinking
I would like to get a foldable tyre maybe 700c x 42? I just cant find any on
the net. Can anyone suggest anywhere that might be able to supply them
within a week? (my frame will support a 42 with brakes etc)
Thanks Kathy

getting quite technical in her old age!