The Secrets of Survival says "There’s no limit to the number of torches you can find during the game..." That means when a torch token is used (either thrown or destroyed), it is returned to the pool of available torch tokens.
Oh right, the 5 must be so every hero can carry one. The wording is strange. We were discarding them when we read it but I get it now. Thanks.
On a side note, while the books don't specify how to track torch hits to the monster, I'd suggest using the Turn/Damage Track.
Actually our book specifies to use the Turn/Damage Track