RAW, you need either a brass brazier or a spellcasting focus.
The material component for find familiar states:
10 gp worth of charcoal, incense, and herbs that must be consumed by fire in a brass brazier.
This is oddly specific language for something that isn’t required at all. The rules-as-written ruling is abundantly clear here: the charcoal, incense, and herbs must be consumed by fire in a brass brazier. Or, alternatively, a spellcasting focus can substitute for the brass brazier only, not the charcoal, incense, and herbs:
A character can use a component pouch or a spellcasting focus (found in chapter 5, “Equipment”) in place of the components specified for a spell. But if a cost is indicated for a component, a character must have that specific component before he or she can cast the spell.
Since a cost for the brazier is not given, the brazier can be replaced by a component pouch or spellcasting focus.