The dragon might be able to shoot napalm using yeast, bacteria, palm trees, and oil sand gizzard stones. The yeast and bacteria make the fuel, the palm trees and oil sands make the gel.
This question goes into various ways that a dragon might produce fire, and this answer might be a good natural reason for your situation. Basically, the dragon would have a sac containing ethanol-producing yeast, and another sac containing sulfuric acid-producing bacteria. These would combine to produce the highly flammable diethyl ether, whose Wikipedia page contains the very disturbing line "It was used as a general anesthetic, until non-flammable drugs were developed".
However, the other requirement you seem to have is that it needs to produce a napalm-like gel substance in order to stick the flames to the target. You say 'napalm-like gel', but why not actual napalm gel? Napalm gets its name from the two chemicals used to make the gelling agent: Naphthenic acid and palmitic acid.
Palmitic acid is the easy one to explain, as it is already the most common type of fatty acid found in animals. To get large enough amounts, just have the dragon's diet be rich in oil palms for some reason. Some biological mechanism and have it store the large amounts of palmitic acid in yet another sac.
Naphthenic acid is a bit trickier, as it is mainly produced during crude oil refining, and crude oil is generally found deep underground. However,
your dragon has hope: the Athabasca oil sands are a source of naphta-rich crude oil that is close to the surface. It's not unreasonable to think that the dragons hang out near exposed pockets of oil sands, using chunks of it as gizzard stones to help digest food. Some bilogical mechanism would separate out the naphta, give it some oxygen, and store the resultant naphthenic acids in their palm oil sacs to create the gel.
The bacteria's sulfuric acid and yeast's ethanol would definitely be an annoying, if not very lethal, poison when separate. When combined, they will produce a short-range burst of flame(if ignited somehow). When combined with the palmitic/naphthenic, it will shoot out as a sticky stream(or glob, your choice) of flame than will burn until it is out of fuel.