The company I deal with here in the northeast, Harvey Industries can actually make any shape window you could want. When replacing odd shapes we make a templet out of paper to match the old window exactly, they use that templet to manufacture the window. I'd imagine the big name manufacturers must do something similar.

If it's a standard sized unit you should be able to get it from any of the big box stores. You need to be 100% sure it's a Half-Round and not an Eyebrow or an Ellipse. I know Jeld-Wen will make anything you want. We install for Lowes and I've ordered numerous types of arched top windows. I agree with Fusion on the template. If you can get a template and bring it in, you'll have no problem getting what you need. Now this would only be the case in a vinyl product, not a clad unit. The only way it would come as a clad unit would be one of their stock sizes. I know Pella has one that is unit sized 29" (W) x 14-1/2" (H). In any case they should have something. good Luck!!!

The issue here, is that you want a replacement unit or sash, as opposed to a full frame unit.
The problem with a sash only, is not making it. That's easy for all the window companies. But they cannot give it any kind of warranty if they don't put it in a frame, to insure it's properly sealed. And no one will build a unit they can't warrant. At least, not the big window companies.
If you really don't want a new construction window, I'd check with a local glass shop, and see if they can make a sash to your specs.

Thanks fusion_866, guy_exterior_man and mike35. Here's how I resolved my circle top problem. I went back to Lowe's and spent an hour with their very comptetent millwork guy. He went thru his literature carefully to make sure he had not missed the possibility of circle tops being offered as "sash". No soap--all manufacturers in his book (Pella, MW) listed circle windows only as "units" . Which is apparently some jargon meaning only offered as built into full frame. With that, and having called another Pella dealer and hearing almost word for word the advice from mike35, I threw in the towel. I paid my money for a full frame MW unit. The bill only came to $335, which was very little more than if I had bought the dbl hung piece and circle piece as sash. So this actually did not turn out badly (I just need to make sure I have a blade for the reciprocatng saw).
Thanks for all the help,
-Lytt

Atlanta Guy....

Next time ask the HD or Lowes Store Manager to whom do they sell their Salvage items too.

In my area of Virginia Lowes & HD sell their Window Salvage to 3 different salvage /wholesale operations. (Believe me the Local General Contractors know where these places are. Just last weekend I saw MW circle tops for $50 for framed fiberglss/vinyl units 4,5,6 ft ones. That could be Mulled to ANY window.
They had circletops, eliptical eyebrows,arches,semi's etc. $50-100 max. They even had Unframed glass ellipticals ready to be framed. Lowe's subsidiary (The Contractor Yard mulls their own MW windows on the spot. ) They don't keep those windows as a combined unit in inventory.

Next time as the staff or an experienced contractor. They don't spend $335 or anywhere near that amount...

i am new to this site and found it really interesting.
could anyone may explain me what is MW unit.
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Peter

Wide Circles