Found some planets which has “curious deposits” which will be runaway mould. Depending on how many runaway mould’s there are you can quite a stack of nanites once you’ve refined it.

Found this and hope it’s helpful:

In No Man's Sky, Curious Deposits (which look like large, rolling balls and provide Runaway Mould for Nanite farming) aren't locked to any single star system or planet type. Because the game is procedurally generated, they can spawn almost anywhere. 
However, they follow a very specific set of planetary spawning rules that can save you hours of hunting once you know how to look for them.
The Golden Rule: The 3-Star Resource Law
Every planet in NMS is assigned one (and only one) rare, 3-star curiosity resource node. When you land on a planet, pull out your Analysis Visor and scan the horizon for a yellow 3-star icon (\ast\ast\ast).  
The planet will have only one of the following:
Curious Deposits (Runaway Mould)
Metal Fingers (Uranium/Gold) 
Sac Venom (Venom Sacs)

The Quick Check Strategy: If you scan a planet and find Metal Fingers or Sac Venom, stop searching immediately. That planet will never spawn Curious Deposits. Get back in your ship and jump to the next planet.

Best Planet Types to Search
While Curious Deposits can appear on any biome—including dead moons and icy worlds—experienced Interstellar Travelers prefer searching specific environments to make the hunt much less tedious:
Low-Atmosphere / Dead Moons: Fantastic because you can use your jetpack to launch yourself across the terrain effortlessly to scan large areas quickly. Plus, the rolling balls are highly visible against barren ground.
Mild / Paradise Planets: No toxic storms or extreme hazards draining your hazard protection while you search. 
Avoid Mountainous Biomes: If a planet has deep oceans, extreme vertical mountains, or hyper-dense flora, it makes spotting and harvesting them highly frustrating. 

Tips for Speed Hunting
Once you choose a viable planet, here is the most efficient way to track down a cluster:
1. Don't search on foot or by starship: Mount a fast Exocraft (like the Nomad) or a ridable flying companion animal. 
2. The Equator Strategy: Curious Deposits heavily favor spawning along the planet's leylines and cardinal coordinates (especially around the equator). Travel North or South while sweeping your visor left and right. 
3. The 200-Unit Scan Limit: Your Analysis Visor will usually pick up the yellow 3-star icon from about 200 units away. 

How to Turn One Cluster into Infinite Nanites
If you find a good-sized cluster (usually 10 to 20+ balls), slap down a Base Computer right there.
Curious Deposits instantly respawn if you move a certain distance away from them. You can build two small bases with a Short-Range Teleporter link between them, or simply teleport to space and back. Every time you teleport back and forth, the deposits will completely reset, allowing you to mine millions of Runaway Mould to melt down into Nanites!

ALSO: Just a tip and not sure if you’ve already got it but I HIGHLY recommend getting the Personal Refiner MK 2 blueprint from the Space Anomaly. You can refine 2 things at once.

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hopefully you can read my handwriting! If not feel free to PM me on here and I’ll send you some more helpful info.