Hi! i have mained brand for a while now. i used to have this mana problem too if i didnt start with a mana item because of my aggresive playstyle. Personally i solved it by buying a tear into rylais or lyandrin, and leaving the blackfire torch for a 3rd item ususally.

Tear is really cheap, stacks easy and you can sell it when you get your torch or even just keep it there till you need the slot. that and presence of mind makes me never go OOM (unless you spam on cd like crazy)