The best place to get them from is the Free Market or Mushmom and Zombie Mushmom drop them except both Mushmom's have a super low drop rate of dropping ilbi's.
illbis can be found if you defeat mushmom.mushmom will drop the illbis about 30% of the time you kill it,that's how it used to be,big bang changed everything so i don't know if that's the proper way of getting it,try it anyways.
kill mushmom until you get illbiis
There's a 5% chance the Mushmom in Henesys will drop it.
You can buy Subis from any potion shop, You can also buy icies, Illbis and other stars from other players in the free market.
Mushmom is a very strong monster for lvl 40. i killed it within 2 minutes with my dexless thief (dexless) 5 mins thief (Not dexless) 10 minutes Warrior impossible, unless its a dex warrior (20 mins) Bowman (Strless) 8 minutes bowman (Regular) 13 minutes Cleric 15 minutes Wizard 10 minutes Aran 20 mins Pirate 10 mins HINT Always jump when he uses his attack ANOTHER HINT HE MIGHT DROP ILLBIS AT A 5% chance