It’s less “surplus” and more stolen. Supply officers figuring out they can sell the gear coming through their post and make multiple times their annual salary from selling them to surplus groups. A lot of poorer countries have that problem, iirc it was a significant part of why the US wasn’t willing to supply the Afghan military with tech.
This collection is a really good breakdown of how the reputation of Spartan society did a lot to carry them through most battles, and how the actual Spartan society absolutely sucked for everyone. One of the things that really stood out to me in regards to how their reputation carried them was that in hoplite battle, you arranged your army by strength from right to left, meaning the right side of your army is facing the left side of your enemy. Essentially the goal of the left side of your army was to survive while the right side of your army was destroying the left side of theirs. Because of the Spartan reputation, it was common for the left side aligned to face their forces in combat would flee before even engaging, leaving an opportunity for the Spartans to flank their enemies and destroy their armies. So Spartans won a lot of battles not because of their immense military capabilities, but because their enemies would allow them to flank based on reputation.