I had the same problem and went to cyclegear to see what they had. They ended up ordering me a yz250 emgo folding lever for $11. Makes a huge difference with my size 12 mx boots.
I had the YZ250 shift lever and loved the extra length. I ended up welding an extra piece into the stock shift lever to make it about an inch longer same length as the YZ250 shifter. The YZ250 lever was better because it stuck out a little more to the side.