Clutch Gear Sprocket Question?

10 tooth is the only size available and even if you could find a bigger one, it would not fit.
Chain rubs with the 10 on some engines as is.
Go with the 36 tooth rear sprocket.

A few things to consider. First, I recommend that you get a rear sprocket adapter to drive the rear wheel hub and getting rid of the spoke driven sprocket that comes with the kits. Manic Mechanic has a nice one. Second, I have found that the 36 tooth sprocket is great on level ground but totally sucks going up hills. If you have to climb hills I wouldn't recommend it. You might try a 40 or 41 tooth sprocket instead, you will get more speed than the 44 tooth and still handle hills pretty well. Third, I recommend avoiding sharp or pointy tooth sprockets and getting flat tooth ones instead. This will reduce drag in a major way and will run and peddle smoother. Also, I use a high quality BMX chain instead of the big 415 one because it runs smoother with less drag (note, you might need a thinner 10 tooth engine sprocket to make this chain fit, depending on the engine you bought). Dax sells the thinner 10 tooth engine sprocket for BMX chains as well as an 11 tooth one that looks thicker for the 415.
That's my 2 cents....