Can you elaborate on which pendants you have already selected. If they are "regular" (not presently on track lights) or track pendants?

They are regular pendants (not made for tracks).

You may also want to try WAC Lighting. They are also doing line voltage flexible track.

Here is a link that might be useful: WAC Lighting

Is there some reason the Lightolier or WAC flexible tracks won't work for you?

The Lightolier system doesn't have adapters for non-track pendants. I wasn't aware that WAC had a line voltage flexible system until ilitem's post.

WAC has adapters, but I haven't been able to figure out if the adapters will work for non-WAC pendants.

Other manufacturers of line voltage bendable track. Capri, Tech Lighting, hampton bay (home depot), Nora, Cooper Lighting, possibly Con-Tech.
Lightolier has the smallest track for ceiling mounting but for suspended track the profile is about the same as other mfg's.

Can you post a picture or URL of the pendant you have purchased? This might help in getting you the assistance you need.

We haven't purchased pendants yet and we're fairly flexible (no pun intended) about the style. Due to the height of the ceiling over the DR table (14-18 feet), our feeling is that the pendants need to be fairly large (12-18 inches long?). Most of the larger pendants seem to be line voltage.

The information on the pendants we liked is on another computer. They are frosted glass and come in two sizes (about 9 inches and about 16 inches). We thought it would look good to mix a couple of smaller ones in with 2 or 3 larger ones.

With all the suggestions Scaly mentioned, we should be able to come up with something, but I still haven't been able to find a manufacturer that supplies an adapter that works with another manufacturer's non-track pendants.

The flexible track manufacturers mentioned above make the item. You just need to wire the fixture into their adaptor. Remember that there is a weight limit for the fixture imposed by the manufacturer. If you aren't sure about the wiring of the fixture into the adaptor, call one of the manufacturers and discuss it with either their technical or customer service departments. When you are looking at the fixture, don't look at the canopy -- you won't be able to use it.