A garden vac? ohhh they suck!
It's got an impellar and a gas engine. It's a big vacumn cleaner. I have one, it's not a big one. I don't care for it.
Using it to pick up black walnuts is a bad idea. They would never make it to the bag, way to big and heavy ( I guess they don't now what baseballs are in Scotland).
Any kids in your neighborhood that would pick them up for .03$ each? 3$ a hundred might sound good to a kid the right age. I don't think you would see him 2 days in a row, but hey it's good excersize.