Are there any soundbars which support airplay?

Not that I've been able to find. If the Soundbar has an Aux in you can buy and Airport Express (AEX) and a 3.5mm male-male audio cable and Airplay to the AEX which will play through the sound bar.

http://www.apple.com/shop/product/FC414LL/A/airport-express-base-station

http://www.monoprice.com/Product?p_id=9565&gclid=CO_fnKrNrcoCFQMJaQodtH0LPQ

AirPlay is fading with Bluetooth becoming the preferred method, it is getting harder to find AirPlay anything. Even if you found one that had it (I did find one 2 years ago but it was too large for where I was going to use it and $6,500, more than I wanted to spend. It really is straightforward, even if you found one you would have to change to the AirPlay setting on it to connect instead you will connect to Aux. Setup won't take more than 5 minutes.

The only affordable soundbar I could find featuring AirPlay are the Libratone Diva (250$ on Amazon USA) and the yamaha ysp 1600 (500$).