The more common version of this request is for flags to be refilled specifically when killing the Titan, which has a master thread here: Auto Refill Titan Flags When Titan Defeated
The counterpoint to these suggestions is that the time constraints on Titans are entirely intentional — they’re meant to make it challenging to sustain and advance in Titan levels, since you have to kill the Titan early enough to have flags for the next one, and sometimes have to decide to let a Titan go to recharge.
You can dislike or argue against that game design element, but it’s clear it was the intention.
Flasks aren’t typically for sale directly, only as part of package offers, and even then in very limited quantity. They’re very rare by design.
They’re not, they currently go to 12*, and 13/14* have existed before but were removed, and will likely return again at some point this year.