The amount of graphite should be about the same - there's a random element to loot generation, so maybe you just heard from someone who lucked into finding a bunch.
Anyway, if you want graphite, you need to check the "misc item" vendors - like Harold in SGS, or Colton/Gort in Junkyard, or Blaine right there by SGS. I believe you can also find it in the inventory of weapons vendors, as well. However, like most other vendor inventory, graphite is random. No vendor seems to have it as static stock.