So far the only discontinued part I know of for these 650's are the little white grommets that snap into the hood. They fit in those rectangular air holes on the sides. As for new aftermarket parts I think they're starting to get scarce. I'm not sure if you can still buy things like aftermarket pipes and ride plates. If so I haven't seen them yet and I've been looking for my ski lol. But you can do a ton of little mods to help wake them up. They are still a heavy and sluggish feeling ski but if you can start mastering stunts with this ski you'll be all that much better on a ski with a bigger engine and more power to weight ratio. Intake grates are still around, pump cones, impellers, aftermarket engine rebuild parts and kits...most of the really important parts are there still.
As mentioned, make sure the crank is good before modding if you plan to...and you most likely will after a month or so of riding. But also make sure to replace the crank seals even before modding, I still have yet to do mine but I know it needs them from how it responds to carb adjustments...it doesn't lol. For the money to fun factor though, you can't go wrong. A SuperJet is how I plan to go next but I stand my ground that it's not worth holding out for a SJ if all you're going to pay is 400-600 for a running ski in decent shape. By the time a SJ in as decent of shape turns up, you'll have enough to get it too and not feel like you've wasted your money on the Kawi. We all started somewhere and for most of us it was the Kawi so join the group lol.