Provided you obtain enough of them and have enough time to cast them all, using 9th level spell scrolls would allow one to cast a lot of 9th level spells without a long rest.
The DMG has rules for granting epic boons (starting on page 231) that include:
Boon of High Magic
You gain one 9th-level spell slot, provided that you already have one.
Boon of spell recall
You can cast any spell you know or have prepared without expending a spell slot. Once you do so, you can't use this boon again until you finish a long rest.
Either of these boons would allow one to cast Foresight (or another 9th level spell) twice before taking a long rest.
Monsters do not have the same restrictions as player characters and it is also possible for them to have more than one 9th level spell slot. An example of this in published adventures is (spoilers):
Acererak from Tomb of Anihilation
1. Suggested by NautArch