I didn't get any return from searching gravity feed soda blaster except for manufactured tools, so here's what I did. Pop bottle with bottom cut off, inverted with hose in bottom. Works way better for the home built soda blaster than the stick with a hose on it. (unless you have 3 hands...)
Also, I made a cheap blasting cabinet from a cardboard box, a piece of plexi I had sitting around, and a furnace filter. Works pretty good! You can't see it but I made little sleeves from an old shirt so you can reach in like in a real manufactured blast cabinet.
I hope this helps, sorry if it's already been posted.