I am pretty sure I read somewhere that they are going to be released in pairs from this point out, not 3 at a time like the original set.
So right now we have 4 and 5
later there will be 6 and 7
and finally 8 and 9.
As the major retailers didn't seem to jump all over these, it may be that we don't see more past that - hell, it may be we won't see even up till 8 and 9