A quick google search lead me to 1aauto.com. The parts you’re looking for are listed under weatherstripping. They do have the Ranger parts in stock (according to the website), but are out of stock for the Cavalier.
A second quick google search for chevy cavalier weatherstripping lead me to partstrain.com, which apparently does have Cavalier weatherstripping in stock, as near as I can tell.
I have no first-hand experience with either of these websites, so I can’t vouch for how well either of them work, nor can I vouch for their customer service, or lack thereof. Hopefully they’ll have the parts you need.