The supply of any product is generally affected by changes in input prices, changes in technology, and changes in expectations. Any or all of these could affect the supply of Blu-ray systems.
The major inputs for these systems are the various metals and plastics that make the discs and players, the labor that goes into making them, and perhaps the costs of shipping them. If any of these increases, the supply of Blu-rays will decline. If they decrease, the supply increases.
The technology in this case is the whole process of creating the discs and players. Changes in technology could include better machines for making the discs or better procedures for making them more quickly. Anything that makes it easier to produce the systems will increase its supply.
Finally, we have expectations. If the firms that produce Blu-ray systems think that something else will make them more money, the supply of Blu-ray systems will decrease as the firms put their efforts towards making those other things. If they think that other things they make are becoming less profitable, they will shift resources to making Blu-ray and the supply will increase.
These are the most likely ways in which the supply of Blu-ray systems can be impacted.