What specific spokes do I need for Giant PSL0s wheelset. I know they are DT Swiss but what kind and maybe where to get them.
Are you building this wheel yourself? There's a bit of planning that goes into building a wheel. As Daniel mentioned, length and gauge are important, but even before that you must have a hub that will accommodate the same number of spokes that the wheel will. Afterward, the number of spokes you will need will dictate what lacing pattern you should use.
As always, Sheldon has the answers.
The DT Swiss site has a spoke calculator at the bottom of the page.
If you are a very experienced wheel builder then go for it. If not, get a pro to do it. Asymmetrical wheels are a whole new level up from "traditional" wheels, with higher tensions, and often blade spokes. From my reading, Sheldon is no help here.
They are nice wheels. Enjoy.
You really ought to be contacting Giant about this, even if for no other reason than to seek clarification of their web page.
The link you posted tells you that they are DT Aero Competition bladed stainless steel, and you don't have to look far on the DT Swiss web site to find these exact spokes.
What your link doesn't say is the length of the spokes. For that, you'll either need to measure them or contact Giant. Note that there will likely be 3 different spoke lengths in play - front, drive and non-drive.
As regards purchasing, depends how many you want to buy and how deep your pockets are. These spokes will likely come out of the factory in boxes of 100 spokes. If you're prepared to buy in this kind of quantity then I'm sure any DT Swiss dealer will be able to help you (assuming, of course, you know the lengths). Again, the DT Swiss site will help you there.
However if you only want one or two spokes then this is more problematic, since most dealers aren't prepared to keep boxes of spokes lying around on the off-chance that they'll sell one or two every now and again. One source I've used in the past is wheelbuilder.com, which was a very pleasant experience (Ca to UK in around 36 hours). There may be other sources which are cheaper/more convenient, but these guys stock your spokes. But again, you'd need to tell them what lengths you need.