Scour thrift shops for vintage ones. These should be cheap enough that you won't mind using them, or just drape over your oven door if it's too cute to risk ruining.
Another good way to get cute tea towels is around the holidays. I've found cupcake towels on sale for super cheap after Valentine's Day and Easter. I got one set from Target last year after Easter, and one set this year just after Valentine's Day.
To find tea towels online, I suggest trying paperchase.co.uk, fisheddy.com or modcloth.com for cute ones. Try Ebay for cheaper ones.
Oooor, if you are really awesome (which I'm sure you are) you could cross stitch your favorite kawaii object onto a towel that's MADE for that sort of thing. I can't remember where, but I saw some towels that were meant for cross stitching on. They had a little grid on them to make it easy. I should have bought some, or at least remembered where they were, damn...