There are loads of custom fireplaces, but I couldn’t find JUST a fire. So here are two of them, re-meshed from Maxis base game fireplaces.
They work like regular fireplaces, except that they can be placed freely (note however that for sims to be able to light a fire, the footprint must point towards an accessible area). Available in Fireplaces for 25§ and 40§.
Fire 1, high poly: 262V/206F
Fire 1, low poly: 161V/100F