1) Stop one is Bead Empire (1032 Sixth Ave between 38th and 39th,) where you will find a good selection of Japanese seed beads, including 8/0 in many finishes. They have Matsunos and also some cheaper ones. You can't always tell, so look at them with care!
2) Stop two is Fun to Bead (1028 Sixth Ave between 38th and 39th.) The have all sorts of strands upstairs, but if you go downstairs they have a wall of small tubes of Matsuno beads for a good price (especially if you just want a small package.)
3)M&J trimming (1008 Sixth Ave) is stop three, which has some hanks of Czech seed beads, but more importantly has more trim and buttons then you will know what to do with. Way fun.
4)Stop four is Toho Shoji (990 Sixth Ave between 36th and 37th.) They have large packs of Mastuno beads and smaller packs of Miyuki beads, in many sizes, finishes and shapes. They also have findings and crystals and other goodness. This one is a favorite of mine.
If you have time for yet more, turn around and go north again on Sixth and hang a right (east) on 37th. As you walk east you will see a slew of shops that stock beads and trimming, so explore! Here are some I have shopped at:
5)Margola, at 48 west 37th, has a wall of Czech hanks. You have to buy the entire hank, so be warned! If you go all the way in, you will see a small wall of seed beads in large tubes. They have some nice 8/0s with pretty finishes, for not much money.
6)City Beads, at 15 west 37th, has a huge selection of Delicas in all sizes and MANY finishes. They are not cheap, but they are not bad for Delicas, and it is cool to see such a nice selection.
7)York, at 10 west 37th, is a tiny shop STUFFED with strands of all sorts of lovely beads. Most are Czech, including hanks of 8/0 3-cuts and other nifty stuff.
8)Phoenix Stone and Beads, at 5 west 37th, had really big bags of seed beads for very little money, in case you want to re-sell. They also have many interesting strands.