Your link doesn't work for me. The KDX250 motor is basically an 88 KX 250 motor w/ a wide-ratio tranny. Reeds for the 88 should work for you.
I found that other reeds, like Boyensen, have part numbers that cover KDX and KX motors of the same year. My Boyensen reeds for my 91 KDX250 are the same part number at a 91 KX250.