I have found 2 good proxies for an Ork Feral army. One for the Orkasaurus, the other for the Squiggoth. Both are from Eureka miniatures, although you have to contact Eureka minis directly for the larger Orkasaurus proxy mini.
I added a few weapons from extras I had left over from various kits and minis I purchased from various companies. Although you could add any suitable weapons for the twin linked big shootas, and the Big Gunz.
I will try to get more suitable weapons for the remaining minis I purchased (4 Squiggoths, and 6 Orkasaurus in all), then get proxy Ork infantry which I found are easily available from the Vanguards Skinnerz range, and then get them painted up.