Voidmetal is a relatively complicated resource to obtain in New World, largely due to its rarity. It'll take some luck, so you'll want to boost your chances of it dropping as much as you possibly can.
Find Voidmetal in Iron Veins
There's a tiny chance of finding Voidmetal when you're farming Iron Veins for Iron Ore, but we must emphasise 'tiny' here.
To boost your drop rate, use the following perks and resources.
Craft into a Pickaxe
While Mining gain 2% chance at finding rare items.
Requires Cooking Skill Lv. 7
Increases your Luck when Mining by 1000 points for 20 minutes. Your health slowly recovers while under these effects.
Minor / Basic / Major
Increases your Luck when Mining by 500 / 1000 / 1500
Mining Luck: Gain 2% chance at finding rare items.
Reinforced Mining Luck: Gain 2% chance at finding rare items.
Adored Mining Luck: Gain 3% chance at finding rare items.
Naturally, farming Iron Veins is time-intensive in itself, but it is the method you can control the most often using the methods above.
Find Voidmetal in chests and from killing Ursus Hortus Bears
The various Supply Crates and other chests have a chance to drop Voidmetal too, and like with Mining, you'll want to equip gear that has the Lucky family of perks to increase your chances of rare drops.
You'll find the Ursus Hortus bears slightly to the southwest of the Settlement in Weaver's Fen. You'll need Mining Skill Lv. 100 to mine their carcasses, instead of the usual skinning.