http://www.zerooneairsoft.com/product_info.php?cPath=268_318_403_494&products_id=8510
http://www.zerooneairsoft.com/product_info.php?cPath=268_318_403_494&products_id=9475
http://www.zerooneairsoft.com/product_info.php?cPath=268_318_403_494&products_id=6076
http://www.zerooneairsoft.com/product_info.php?cPath=268_318_403_494&products_id=8521
http://www.zerooneairsoft.com/product_info.php?cPath=268_318_403_495&products_id=8519
Take your pick really.
The receivers on them are polymer, and are super rugged, so won't break easily. They all have V2 gear boxes, so plenty of aftermarket parts.