It is called The Ultimate Car Seat Travel Bag by J.L. Childress. (theletteredcottage.net)
You could try a cart or wheeled car seat travel bag like this to lug your heavy seat around, or invest in an inexpensive and lightweight seat just for travel — the Cosco Scenera is a good one. (havebabywilltravel.com)
If you take your chances in hopes of a seat, or must bring your seat and check it, I highly recommend purchasing a padded car seat travel bag, and gate checking it. (havebabywilltravel.com)