I have used Atkso silicone waterproof spray on a lot of gear and been very satisfied with its performance.
It does smell a bit when you spray it on so you have to hang it out in a garage, Once fully set there is no smell.
I have seen it at some cobblers shops or motor bike shops. I bought my spray from globetrekker,
Cheers
Paul
http://www.globetrekker.com.au/brands/Atsko.html