Just ideas that might lead somewhere...
The best I can think of at the moment is something like an ordinary wood cutting tool. A grooving plane would probably be your best bet.
A spokeshave or a plane set to a thick cut and used on the edge of a thin sheet or strip of wood might work, especially if you've just used a grooving plane on it. Not exacly chips but the shavings would crumble easily enough.
An auger bit makes chips but that would be a painful way to fuel a stove. Even a twist drill makes a sort of chip when drilling wood.
A properly sharp chain saw makes the sort of chips that you might be looking for, and a router can too, but you said manual. I suppose a pole lathe would be getting a bit silly.
If you know of a firm or have a friend that does wood turning they might have loads of scrap wood chips.
...ooOoo...
I've never used wood pellets in my Bushbuddy, I just break up little twigs and it works fine as long as they're good and dry.
As has been pointed out for the amount that you'll use cooking on a woodgas stove you may as well pick up a sack from the supermarket.