No exception. No you can't say "mit meine alte Mutter" it must be "meiner alten Mutter" and definitely never "alter Mutter", the latter isn't even a thing (sex mismatch). And also never "dem altem Vater" it is "dem alten Vater". Now that latter one makes me wonder, it is a surface transformation not a deep ...
No, it doesn't exist. It's a typo and should read:
Diese Substanz wurde [...] angegeben [...]
You can find it in this Wiktionary flexion table at
Präteritum > Vorgangspassiv > Indikativ > 3. Person Singular
It is Dativ.
"nach" is always followed by a Dativ, and one way to use "suchen" uses the word "nach" to mark the object one hopes to find.
It is also possible to use "suchen" without "nach". In that case, the phrase would be "wir suchen trockene Rinde", where "Rinde" would be an Akkusativ.