These guys should be able to locate a manufacturer for yu Steve.
http://www.poleclimbing.org.uk/
They look like modified cycling shoes to me.
I've had silly thoughts of making a pair of toe spikes that would latch onto my wesco's, but I want them to swivel up and lock into safety housing on the boots lower tongue. Lock down to climb, lock up to trim. It needs a steel receptor plate on the lower front soul of the boots toe.
I think copying a cat's claw with thick spring grade steel would work and do far less damage to the bark and cambium than traditional tree gaffs.
It would be a neat project requiring a boot experts help.
jomoco