You can get similar pulls in a bunch of places. You can find some at:

http://www.richelieu.com/en/decorative-and-cabinet-hardware-1004221-c?id=1004221&page=1&imgMode=l&f=1&c_6375=1025168&mode=pull&idGr=1004315&selectGr=1

As for the sizes, this was based on the desired look at the time. There isn't a particular rule of thumb. Some people prefer the handles to be longer to give that linear look, others prefer the handles to be smaller and more discreet. The orientation of the handles is another factor and finally budget. The longer the handles the more costly it can become by time you've added all the doors and drawers together. Recently I've opted to do no hardware on the upper cabinets (finger pulls instead) which gives a cleaner look. I've spent the budget on nicer longer handles on the lower cabinet instead.

I'm putting 36" cabinets and looking at these exact pulls. Would 8" or 6" look better since there's also cabinets on top?