If you are looking for the german flamethrower, you should find it on Pavlov and Valirisk in a couple of minutes as they are spawning in the mainbase. There are more maps where you can find it though (such as battle of stalingrad, counterattack, Fall weiss.... but I won't list all of them
).
If you want to edit some spawners, all you need is a notepad, and a software to pack and unpack .rfa files.
I'm using winRFA to unpack, and GUI_RfaPack to pack them. Make sure to always have a back up of your maps before you edit them, as it might screw up your game.