Mine didn't come with a rear cap so I just keep in on the adapter with a spare Olympus rear lens cap. I find the best deals on front caps are either from Adorama or BandH. Kind of stinks if you have to pay shipping though. 55mm isn't that uncommon so maybe you can find a front cap at a local store.
I would be curious as to what adapter you are going to use? I'm really not crazy about the one I bought.