Q:

Can you learn portions of Avot D'Rav Nattan on Tish'a B'Av?

This M.Y. answer provides a list of permissible learning items on Tish'a B'Av. All these items are somehow related to the themes of mourning, the Temple destruction, etc.
Avot D'Rav Natan has several Mishnayot that seem to relate to the theme of Tish'a B'Av related to the setruction of Jerusalem. Examples:
Avot D'Rav Natan 4:4 and 4:5 
Rav Yohanan ben Zakkai's request from Vespasian for Yavneh
Avot D'Rav Natan 6:3
Near the end of Mishnah; story of Kalba Savu'a who had enough  food to feed everyone in Jerusalem for 22 years. Yet, the Zealots destroyed his storehouses
Would it be appropriate to learn these? Why weren't these included in the list?

A:

Tanna v'sheeyer - Anything fitting the mood of the day is acceptable (at least without iyun [in-depth analysis]; see also sources cited by @WFB in comments below which are lenient even with regard to iyun). It would be impossible to have a comprehensive list since Torah SheBaal Peh (the oral Torah) is constantly expanding. (My assumption is that these specific passages were also not included in the list because they are relatively short.) See also, e.g., the Aruch HaShulchan (554:5) who permits reading the sad passages in Neviim left unmentioned by the Brayta:

ויראה לי דכן דברים הרעים שבשארי נביאים – מותר לקרות. ומה שהש"ס חשיב רק ירמיה – משום דבירמיה יש הרבה דברים רעים.
It seems to me that, so too, one is allowed to read the sad passages [lit: bad things] in the other Prophets and the reason the Talmud only mentioned Jeremiah is because there are many sad passages in Jeremiah.

(This inclusive understanding, by the way, is the basis why later codes and commentaries [e.g. Levush cited by Mishna Berura] added to the original Talmudic list.)

