Location, Location, Location. Outside of T4 and some T3 stuff, I can find just about everything in ICS Alpha Terminal in Attalica or Truhold-Markson Alpha Terminal in New Virginia. Independent producers in PO are going to go to popular hubs so they can sell their product. Trying to sell equipment in less active terminals can take a while and most people want to produce the product, sell it, profit, rinse and repeat.
Switching gears a little bit to ore instead of equipment, I like to mine in a less populated area and it great. I have no problems finding ore but when it comes to selling it, it takes me about 20 minutes to reach a “popular” terminal to sell my ore, and as Winter stated above, the only fix to the open market is having a bigger community and expanding outside of main hubs to sell. Something like this will just take time.
By the way, you mention slaving yourself to some megacorp for equipment but that isn’t the case. PIE for example has helped me out quite a bit and we are far from mega.