If you are not able to obtain a candle or even light it. Use a fabric or paper that has the color red or orange. These colors are warm and passionate- like fire. You can even have a photograph or drawing of fire. Whatever works for you.
You can look up and or draw sigils for fire. You could also just have a picture of a fire. There's also electric candles if the problem is having actual candles.
If you can have candles, tea lights are really cheap and come with multiple ones.
Wood could be used to represent fire but more likely earth. In some systems, wood is actually an element in itself. If you want to represent fire,I would recommend a lamp or candle though.