Dude, find a wireless hotspot and get your hands on that Victini. Victini is a very potent threat early on in the game, and can easily KO the Bug Pokemon with Incinerate, and kill the 'Pede Poison/Bug types with Confusion.
This isn't to say that Victini is broken in-game, because it isn't. A slow Experience rate paired with (fairly mediocre) dual STAB that will only have about 50 Base Power until the late 40's (Stuck with Flame Charge and Confusion for the majority of the game, unless you find some good TMs) dramatically dumbs down Victini's 100 offenses.
If not though, take the Darumaka just for that gym battle. Using a Pokemon only once to make a gym battle easier is no big showing of shame or anything (Hell, I dropped four of my Pokemon so far). Just keep your team flexible, because frankly, a Fire-type isn't required for a good team, nor is any specific type.