How to find or buy Antimatter
Antimatter can be found as a potentially random drop in chests and the like at outposts that you find on planets, or occasionally in chests at space stations. If youre following the Atlas story path the game will also funnel you towards a free one to get you started. Others can drop at random, but there is an easier way

That aforementioned easier way is to just buy antimatter. While it isnt available at every single galactic trade vendor, many vendors will carry a single or a couple of units of antimatter. Its expensive, costing over 50,000 credits at is basic price, but for such a rare resource its worth it.

How to craft Antimatter
Your first ever Antimatter should be rewarded to you by a friendly alien as part of No Mans Skys main story quest which the game gently guides players that choose the Atlas Path through with objectives.

After that however youre on your own and youre going to need a heck of a lot of them for your journey. Eventually the expense will become too much to regularly expend on buying them too but thankfully an alien in your second star system will also give you the crafting recipe so you can get making it.

[quote]To craft Antimatter youll need:
1 Electron Vapour. This resource is crafted from 1 Suspension Fluid (Available for purchase from space stations or crafted from 50 Carbon) and 100 Plutonium (Readily available to mine on planets or also sold in space stations). The crafting recipe is unlocked from the moment you start the game.
50 Heridium. This resource is available planet-side but also happens to be frustratingly rare. It can be found as part of very large rock deposits, so fly low over a planet in your ship and keep an eye out for colossal rocks if you find one, theres a strong chance its an absolutely huge Heridium deposit. You can also just buy it from space stations, but its comparatively expensive.
20 Zinc. This is another planet-side resource but is more common. Its found all over, though in the systems Ive traveled so far its most commonly extracted from certain types of plant. Its also available for sale in space stations.[/quote]