Andy
I was just chatting with a Canadian who suffered a cracked piston on his traxter, I looked on ebay and was surprised to not see ANY pistons. I looked at my distributors and also nothing, at this point I do not know if no one fixes them or if it is more the case no one CAN fix them because parts are unavailable. There are companies who would make pistons but expect to need to buy a batch just not one. This is likely why no one has them it is just not viable to buy a batch for one piston or to sit on a shelf and not sell because no one will fix the machine.
If there were enough people, I am sure we could get a group to buy a batch. This is not a fast process especially as we get close to motorcycle riding season. The stock piston appears cast and you would end up with a forged piston which would be stronger than stock and could also likely have higher compression for more power though don't expect too much based on design. The cylinders are Nikasil coated so you could use a drop in piston but I always recommend you re-nikasil to get a best fit of piston to cylinder.