I would tell you to go for the Tokyo Marui MP5K, but obviously it's plastic. If that's not a huge issue with you, this gun is my favourite gun of all time. Check out my channel if you want to see what it's truly capable of. This is where I bought the gun:
http://www.airsoftworld.net/tokyo-marui-hk-mp5k-high-cycle-airsoft-smg.html
Good luck finding one. I love MP5s.