I just heard back from Merck and they said "Footvax has been discontinued and our inventory is depleted."
Does anyone have any other sources?
Is your ground particularly boggy?
If not, Id suggest you start culling hard for feet - if something goes off its feet, trim, spray with terramycin or alamycin spray, mark and sell as a cull - try not to keep its daugters either, in a few generations you will have minimised your foot problems, some sheep seem naturally resistant to the footrot bacteria.
I do this and only buy off people who have this policy and this summer I can count the number of limpers I have had on one hand.
I know it sounds like a long slog, but your flock will be better for it eventually.
If hey are *all* limping then you might have the wrong breed for your farm, different sheep suit different places.