If you want a 12 inch wheel, the only trike I know of that used it was a Tri-Z.
Alot of guys have played with honda hubs and 250R-350X 11 inch wheels and got them on a Z front end, so I would guess that you could probably adapt the Tri-Z front hub and wheel over to your 350X with some axle spacers custom made to center the hub up, and you will have to work around the brake caliper spacing to get a 350X front caliper to mate to a Z rotor.
Here is where my long useless list of stuff nobody cares about should go...
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