For this type of window you usually position the rod under the half circle part at the top. Heavy drapes only cover the bottom portion of the window. They make sheers to cover the half round part if too much sun is a problem. These are gathered at the bottom center of the half circle and radiate up and out.

Where to shop is dependent on your budget and taste.

You might get more advice if you post pictures of the windows and the rest of the room. We are all very visual. : )

I have similar windows, and while I don't have curtains yet, my plan is to put knobs (about 3 each) on either side at the very top of the window and hang full, floor length drapes from these knobs. The curtains won't be working, but they will soften the room. I don't want to put a rod under the arched window b/c I feel it would shorten the window and to put a rod at the top of the arch would compromise the crown moulding. It has been an issue for me, which is why there are no draperies yet in my dining and living rooms, but this is my plan when I finally go for it.
Good luck with your decision!