Id be tempted to get a protein blend and mix it with ground rice personally.
Or give this a go.
http://www.myprotein.com/uk/products/total_gainer
http://www.myprotein.com/uk/products/weight_gainer_elite
Both wheat free.
Or give this a go.
http://www.myprotein.com/uk/products/total_gainer
http://www.myprotein.com/uk/products/weight_gainer_elite
Both wheat free.