Is there any shops selling Prepaid 4G Card at xiamen airport?

Yes, as far as I know, you can buy the sim card in the airport. But I'm not sure whether it's 4G or not.

The service counters are located at the Exit of International Arrival Hall, Terminal 3 and Boarding Gate No. 10 International Isolation Region. Usually a new SIM card costs CNY100, with the card itself for free and CNY100 as your deposit. Anyway, you can check on the spot.