First off I dont know where you get your info on the wheels. Excel makes and list the wheels for the bike. You have to buy the 18x2.15 or 19x2.15 rim and matching spoke/nipple kit. Any dealer or parts house can get you those items. Then all you have to do is lace and true the wheel on your stock hub. It is the same hub for the 90-91/2(?) kx, but all the 89-02 wheels are interchangeable on the KX/kdx250s.
For the radiator guards, the 90-93 kx250s work. But hte stockers are fairly cheap through the dealer.