I have two clients who are asking for responsive sites and others who are starting to look at it. When will the responsive editor be available?

If you have the HTML Editor, check out the responsive themes for it:
https://www.coffeecup.com/store/themes/ … or-themes/
Responsive forms and sitemaps are there as well. Other items are soon to appear.

I appreciate the themes that are already set up that way, but I have complex custom layouts for my clients. I need to start from scratch.

I have thought about purchasing a responsive theme and then trying to break it down. I went to the CC store, but it only let's you see a picture of the full size theme, not what it looks like at lesser widths. Any idea how to see the "responsiveness" of themes for sale?

I don't think there are any previews.
There are many responsive grids available now, maybe check some of these out and see if any suit you?
http://www.getskeleton.com/
http://foundation.zurb.com/grid.php
http://www.responsivegridsystem.com/
Google responsive grid or framework and you'll find many more.
I've used the 3rd one listed for a few sites and really like its ease of use.

I was under the impression that the current version of the HTML Editor includes at least 1 responsive theme, maybe check there and see what it looks like?

There's one HTML 5 theme with a fluid layout and a few fluid templates (2 or 3 column).

A responsive grid would give you a lot of flexibility , allowing you to create your own design.

Brian, since it is not possible to view the responsiveness of the themes, take a look at this very site, and try to narrow down the viewport.

What you will see is that columns next to each other merge into fewer columns, contents that used to be next to each other get placed below each other, images get smaller, the navigation menu shrinks until it collapses into a dropdown menu.

The principles of the responsive technique is always something like that, and you can decide what chunks of contents you want to have first, second etc.

Another site (work in progress) to look at could be www.eikweb.com/test