After putting my thinking cap on I figured, why not just make one myself out of cardboard? I had a couple of boxes in the garage from online shopping and some SWEET Colored Duck Tape my mom had given me for my birthday! I measured and the hopper was not a perfect square. It was about 8"x8.5" - Just so happened one of my boxes was 8x8x12. I cut the 8 inch sides and left the folded part. The folded pieces would be cut on an so they would lay flat on the angled parts of my current 7lb hopper (see the picture to follow what Im saying). I then cut the 12" sections to 8.5" leaving the flap as well. Then I taped it all up and placed in the hopper to make taping adjustments. The design assumes that the weight of the grain on the flaps will keep the hopper in place... I have NOT test this yet :)
(Extension laying flat for easy storage)
(extension on top of 7lb hopper)
The Extension itself its 8"x8.5"x8" which comes out to 544 inches cubed. A pound of barley takes up about 46.2 inches cubed. So this roughly gives the extension a capacity of ~11.77 lbs (544/46.2). So to be safe we will say my total hopper (original 7 lb hopper and extension) can probably hold a total of 17-18lbs. Most recipes I brew don't come in that high. but I will be sure to test this extension out next brewday and report back.