Does anyone know whether there is 1:72 scale P-8A Poseidon kit available?

Welsh Models does a 1/72 737-800. Contrails has a conversion in 1/144 which will show you what's needed. You'll need new wingtips, various lumps, bumps, pylons and fairings, plus of course the bomb bay.

Thanks Jessica, I will certainly check into that. I am building a 1/72 scale history of the squadron I used to fly with (VP-5). They first flew the PBY Catalina, the PV-1 Ventura, the P2V Neptune, the P-3 Orion (which I flew in), and in early 2013, the P-8A Poseidon.

Aha! Look at what I just found!
Problem solved

Thanks Jessie!
Is this a 1/72 kit?

Yes it is. Be warned that it's not exactly cheap.

How mush in US $?

Never mind, I found the price. $157.64 U.S. dollars, wow that's a lot. I can't ever remember paying that much for a 1/72 scale kit.