hi Alex. I took a quick look at archive.org, they have quite a few editions of Under the Red Robe. From just a fast glance, it looks like *maybe* the images in the archive
http://archive.org/details/underredrobe00weymiala *might* be the best quality you will get (though they still are not excellent, reproduction methods were not the best back then for paintings and photos).
To get the scanned pages -- on the "download" page for each archive, under the list of formats offered, is a link for "https". This will take you to the FTP page, and you will find a list of files. Look for the ones that end in jp2_.zip, or jpg_zip. The image zip files are quite large, and sometimes very slow to download (often 20 - 45 minutes!)
Use the "read online" feature to view the book, and download the ones that look best to your eyes. Then the only thing you can do is open the zips and take a look at the actual scans and pick the best ones. Sometimes, it is better to use individual pages from several different archives (when available).
The actual physical cleanup and re-sizing depends on the image editor you decide to use. As you know, I use PaintShop Pro, and not too many folks do. Lots of people use the GIMP for free, or Photoshop (pricey!). There are lots of freeware image editors out there, many very highly rated, such as PaintDotNet.
In general, you usually need to either completely desaturate the image or convert it to grayscale. Then maybe adjust the contrast, then clean up scratches and spots, and downsize the image. Keep the image in a lossless format, such as bitmap or (photoshop) psd, until the very end, even though the file size will be very large. Jpeg is lossy, and you will lose quality every time you re-save the file.
(I haven't forgotten, I'm still plugging away at Innocents, but not much free time these weeks)
EDITED TO ADD -- PS --The image you posted is pretty bad, though I have worked with worse. The only fix for something like that is to literally restore it using clone brush and smudging, and dodge and burn (yep, like developing photos). Sometimes you can't tell if the flaws are due to dirt and damage, to scanning artifacts, or if the artist actually drew it that way, very frustrating. It takes a lot of patience and sometimes the end result just isn't worth the time and effort.
The attached samples from a book I worked on once show a fair amount of improvement, I think, but I don't know if it was worth it. But at least now the man in the corner actually has a face.