ETA if you can't find one, I wouldn't worry about it too much. Having to put the stroller in a bag was a PITA. I hardly ever see strollers in bags when I fly.
I clicked on MoM by accident, but I have a JL Childress stroller bag and it handles a city select with two seats plus a random coat or blanket shoved in there. It's just canvas so it's more to protect against dirt and scratches than to prevent serious damage, but I've flown with mine on a dozen flights and its held up well. My stroller is still in great condition.
Idk if you can buy them at bru, I got mine on Amazon.