i need it for my magmortar
Flame plate is a good booster, (1.2x) you can get one in the underground, the one you recieve in game is in stark mountain (after pokemon league)
Try the Fire Plate. It is hard to get and it is for Arceus, but it really boosts fire type moves alot!
Charcoal, it raises it by 20%,
Flame Plate and Sunny Day, I think gives boosts