The 250SX ignition switch maches the size of a few other machines, 250es for example is the same "core" just different wiring/connectors. I haven't personally taken apart a 250sx switch since all of the ones I've had were good, but I do buy new Honda switches and change the wiring to be plug and play for the ATC250ES. I guess this is kind of aftermarket, even though Honda makes it and I mod it. I've linked my 3ww shop listing below, I also have them listed on ebay.
http://shop.3wheelerworld.com/index....product_id=392
Should be the closest you can get to NOS you can get.
Anyway, if you still wanted to try to take yours apart, the very bottom is like a disk, and the rest of the housing is a cinder. There's 3 tabs on the disk that hook into the cinder, get the housing to clear the tab and it pops out. Inside should be 2 contacts that are spring loaded tied to the key system inside. Based on the Chinese switches I take apart, nothing should just fall out, but careful about the part that moves with the key as I'm pretty sure nothing really holds it in except a couple spring loaded ball bearings to make the "click" effect. If the contact rivets on the disk look to be savable, sand them down and try to use something with a high grit number like 400 to finish it. The upper contacts could probably be touched up the same way. Normally there's like a nub that sticks down from the top contacts, if that nub wears out, it's connections might not be reliable and probably should be replaced. The new switches I get are packed so full of electrical grease that it's oozing out so the OEM ones are probably a mess inside. I'm not 100% sure what kind of grease they use, I'm thinking it's some sort of white lithium grease.
Now the real question comes up, why do you think the ignition switch is bad? Like have you tested it with a multi meter and validated it's not getting connection? I'm not all about getting sales, if you don't need the part, no point in throwing money away unless you'd like to have the fact you know it's a new part so will be more reliable than an old part.
Test for the ignition switch is as follows:
Off = Black/White and Green connected together
On = Red and Black connected together
Easiest is to use a multi meter on the Ohms or beep setting, but you could do it with a battery, test light, and some hook up wire to run power though the switch to light up the light.
Good luck and let us know how things work out.