Personally I don't use dextrose. At the moment I don't do any of the PW shake business either. Just eat real food. Somewhere on here there's an article that says women don't benefit from dextrose like guys.
Dextrose is basically just a really simple carb that can be quickly absorbed, as you would want post workout to help replace the glycogen you burned up. You might be able to get it at a GNC of a health food store (powder form) but I recall the one time I went looking for it I ended up ordering on line..
You can google it to get more info.