Try Y's bikes. there are about 3 or 4 around Tokyo; there is one near Roponggi for sure. I think Aoyama Itchome but you'll have to check. I also ride a track bike and I know its hell getting anything. There is a decent bike shop in my city but they're a little overpriced and I when I was putting the bike together I had to custom order everything because they didn't stock many parts. I did find some used Nitto track drops in a bike shop in Shizuoka for 1000 en.

anyway good luck