Is there any advice about making the 100 brachos on a fast day?
It is possible to make up the missing blessings by making berachos on pleasant scents. Additionally, one should answer the blessings over the Torah and blessings of maftir with intent, and these berachos can also be counted.
For Tisha Be’av, some write that one should not take pleasure in fine scents, and that the blessings can be made up with asher yatzar, and by answering berachos as noted above..
Sources: See Mateh Efraim 632; Mishnah Berurah 46:14.