I haven't really had a need recently for Baby Cat. Thankfully the rescues are all holding their own without needing this.
I'm told Petcurean's Now! Fresh Kitten is a similar size to the RC Kitten (which is larger than the baby cat). Unfortunately this brand is difficult to find in stores (I buy the Senior variety online).
I know this news has left several people struggling to figure out what to replace the Baby Cat with. I don't know if anyone has reported finding a similar sized product yet.