Assumedly, you understand the Craft: Alchemy rules out of the core book, so ...
It's up to the GM:
1. How much game time to spend on acquiring materials
2. How to limit the alchemist's arsenal
For better play balance and to not waste other players' time, I've just alloted finished goods to a PC that I thought were reasonable given the character's approximate financial state at the time. But, I tend to be antiminutiae.
I have nothing per se against creating adventures to get materials. There are some problems with it, however, that deserve at least some consideration. One, until the adventure reaches some point, the character lacks the weapons. Two, the amount that the character acquires is likely to be problematic in that if there's not enough to sustain through future adventures then no real purpose was served and if there's too much then it becomes trivially easy to have too many bombs. In other words, ideally IMO, the character should have a reasonably consistent amount of explosives adventure to adventure with the occasional lack of stockpile, something that's highly unlikely in any sort of realistic situation where someone is either likely to be starved or is going to be overflowing with materials. Three, how many of these sorts of adventures are interesting to everyone else?
Of course, any wealth generating adventure can be turned into buying or bartering for alchemical goods. And, this all assumes that the alchemical character has fireballs during normal adventures and not just in "special, my schtick is alchemy, so I have nukes when nothing besides nukes will smoke the adventure's obstacles" adventures.
