Whipped Dog sells knots too. They are very low cost, but as I have never used them I cant say anything about the quality. TGN and Shavemac are the usual suspects though, and I can recommend the knots at both.
I just got in one of the Whipped Dog 22mm Best Badgers and put it in an old rubber set restore (I'll post pics as soon as I get the computer up and running after a virus).
Compared to the Crabtree & Evelyn Best Badger I am using this knot is denser and softer yet has much more backbone.
They are well worth the money. Plus he guarantees you'll be happy or he'll refund your money.
I have two more handles waiting for me to get the funds and I'll be ordering from Whipped Dog again.