Fabric lines always do this. Trends come and go. Types of designs and prints that were plentiful a few years ago are no longer made and other things become popular. I did find a few wildlife flannels with a quick google search like this:
http://www.cozymountainquilts.com/catalog.php?item=2430 and
http://www.cozymountainquilts.com/catalog.php?item=2428
So you may need to get creative to do a theme quilt. Maybe instead of finding fabric prints that depict wildlife try finding some block patterns that depict the wildlife instead. There are many paper pieced patterns out there as well as traditional piecing methods. I have seen bear blocks, fox, owl, deer. Some are simply pieced and some are very elaborate.
Here are some links to patterns I found
https://www.anniescatalog.com/detail...kCEaAvwv8P8HAQ
https://sewfreshquilts.blogspot.com/...n-release.html
silver Linings has tons of PP wildlife designs
http://www.silverliningsoriginals.com/
While many of these would be an effort in frustration to do in flannel, you can always make your top out of regular quilting cottons and back in flannel.
I have successfully pieced and PP with flannel but used much simpler designs.