mc21 uses the same discs as the cbr250rr and I'm certain ebc makes them for the cbr.
http://www.wemoto.com/bikes/Honda/CBR_250_RRL_RRN_RRR_MC22_Japan/90-94/picture/Disc_Front_EBC_-_Left_Hand/
or
http://www.wemoto.com/bikes/Honda/NSR_250_RL_RN_RSP_MC21Japanese_Market/90-93/picture/Disc_Front_EBC_-_Left_Hand/
I have heard a few bad reports about the chinese ones too, warping etc. so it's a bit of a gamble.