Help! My lock and lock has come adrift

Can anyone of you lovely bunch help me find a replacement lid for my lock and lock bottle. It's the one from this set: The little seal inside the bottle screw cap has gone missing and now my bottle leaks *sniff* As I bought this set from Australia, I can't get one the same in the UK and nothing else fits in the bag with my boxes. I can't pack it any other way round either as the bag is designed to stack the boxes one on top of the other with the bottle being on its side on top. I would be so so grateful if anyone can help me find a replacement and I will gladly swap something in return. *fingers crossed*