You're probably right about the shaft size. The pinion would likely need to be drilled out to fit a 1/8" shaft.
The real gear is a (LE-Gear10) from Leisure. The 10t Pinion Gear was about $2.50 but they raised it several months ago. Kirk had raised his price to around $4.
If all else fails, Kirk would give you the number for Leisure. I didn't find a link.
Here is the MEC link:
They don't list the 10T pinion seperately so you'll have to call.