Haven't seen AA pass out any customs forms since last year, may have just been the flights I was on but don't expect them. Last time I went down the station did not have any government distributed forms but were handing out locally photocopied black and white customs forms. If you use the online site it sometimes has problems with the chrome browser but seems to be tailored to the MS Edge browser
shakehead
. Select airport of entry as Cancun and the terminal of cozumel (Cozumel customs is under the Cancun office).