I'm going to be the odd man out here and say that I don't think you need a cam to make a zigzag on that machine. I have a Dressmaker SWA-2000 with guts that look very much like yours. I don't have any cams for it, but it will make a zigzag...almost. First, this is what my machine looks like (is yours similar?):
[ATTACH=CONFIG]509062[/ATTACH]
Mine has a plastic gear that drives the zigzag mechanism, which is circled here:
[ATTACH=CONFIG]509063[/ATTACH]
The gear on mine is cracked all the way through, but hasn't broken off yet which my best guess is why I am getting a scalloped shape when zigzagging, demonstrated by blue and black stitches here:
[ATTACH=CONFIG]509064[/ATTACH]
Also, in your photo, there appears to be the end of a wire (or end of spring) that is clipped onto the edge of the cam follower. If you can see in my photo, there is no such wire clipped on the side of the cam follower. Yours also appears to be loosely wound around the base of that cam follower and mine doesn't appear to be that way. I'm not sure how that actually works...so it's entirely possible yours is correct and mine is not. That's just the only difference I notice. But, there's no way for me to check mine for function without any cams.
Could you also post pictures of your machine and the cams that go with it? It helps others identify machines/cams. There is a good thread you could post those pics on here:
http://www.quiltingboard.com/vintage...d-t252968.html
There is a yahoo group called vintagejapansewingmachines where I did read some discussions about replacing the gear on my model with one that is apparently still available, but I haven't pursued that. There are people in that group that can probably help you more than I can. I became completely unimpressed with this machine and a Morse with cracked cams/gears.
Good luck.
John