It does appear there may be a market, no doubt a small one, but a market none-the-less, for contact printing frames in the banquet sizes. Or, at least a frame capable of handling 7x17 and 8x20 negatives.
A NOS (new, old stock) AWB 10" x 22" contact printing frame sold on eBay this morning for $237.50. From, the photos that accompany the auction, one of the corners has come unglued and will need to be re-glued by the new owner. The frames I will be selling have reinforced (splined) corners to prevent this from happening.
The frames I will be selling are made by the camera manufacturer Argentum. They are very well made from high quality materials. The wood is white ash (the same straight-grained hardwood use to make baseball bats). The actual imaging area is 1cm larger in both direction than the nominal frame size. So, the image area of the 24x30cm frame is actually 25x31cm (9.8" x 12.2"). So, a 24x55cm frame for 7x17 and 8x20 would have image area of 25x56cm (9.8" x 22").
I'll try to get some pictures of the 24x30cm frame posted in the next day or two. In the mean time, here's a link to a pdf file of the contact printing frames page from the manufacturer's printed catalog.
Really Big Cameras