I found a replacement that works for these discontinued replacement heads! The heads fit onto the stem of the Casabella dishwashing brush, and they’re cheaper than what Casabella used to charge!!! I’ve used the heads now for over a month (and I do dishes at least a few times a day), and they’ve been great!
The replacement heads / refills are the Munchkin 2-piece Shine Stainless Steel bottle brush refills. They sell on Amazon for $4.49 for two (cheaper than one of the Casabella ones used to be!). I’ve shown the two brushes below, so you can see the Casabella (green) one is much longer than the Munchkin. For me, I need the length to wash bottles that are bigger. But I ordered the full bottle brush from Munchkin, just in case the replacement heads didn’t fit, so I would still be able to use the new brush. Now, you don’t have to!