There is a "flip-top" pattern on www.knittingpatterncentral.com
. It's on a site where you have to register to get it, but it's completely free. There may be others on there, but I couldn't tell from their names. . .you might just need to look at a bunch. Also-- if that pattern, above, isn't for worsted weight or the correct size, you could probably just get the idea from the directions and then make it work with a "regular" mitten pattern in the size and yarn weight you like. Also, try www.knitty.com
. They have a pattern for "convertables", that is, gloves which have a mitten top which flips back (it's called Broad St Gloves), but they may also have flip-top mittens-- it'll just take some sifting through their list as well.