The last time I tried to help someone with Herring discount codes here I ended up getting nothing but abuse from the guy, but here goes.
I don't know of any codes with that big a discount, but there used to be a standard 10% off code, TWEET10, that worked most of the time.
You could check Herring's Twitter for anything else. They often have codes for specific shoes.
There's also a code for free shoe trees on Herring brand shoes. Go to AAAC and you'll find it.
Unfortunately you cannot combine the codes. Else it would be a neat deal.
So depending on the item price and the need for a shoe tree the AAAC code will in some cases be the better code to use.