I used to work at a lingerie store, and I was their bra specialist and also intimates supervisor. There is something called a sister size- we used this method when we didn't have the colour/model in the size the customer was, but we could do a little math to make it fit. The sister size to a 30E is a 32DDD, and the sister size to a 30F is 32E. This is generally what most bra retailers go by, and these are also US sizes, I'm not sure about UK or other countries as I've not looked into it. Hope this helps you if you can't find any 30s, it can be a difficult one to find, sorry :\