Weak Fire Runes need a Sunstone along with a Blank Rune and a Silver Ingot to make one Weak Fire Rune.
Weak Runes can be crafted at level one at the Rune Altar.
You need three of these to learn Flame Blast and you will need extra to cast the spell.
The command to make a Weak Fire Rune is [nya!rpg rune altar weak fire]. For more info use [nya!info weak fire rune].