I'd recommend checking the wiki as it notes there are a few options to use the skill Greed and often it is worth checking the wiki in addition to the forum for details like these.
But to answer your question, you can use this stone to enchant a lower costume with the skill. Costume stone enchants have a 50% chance of attaching to the costume, so some players choose to buy the costume with the enchant attached if they don't want to gamble.
As for regular gear that gives the skill, there are two garments you can equip for Greed. Heroic Backpack is what many players choose to get access to Greed. A bit harder to find would be a Greed Amistr Bag but also works and has a small buff to drops and exp.
Greed can also be autocast by a few upper headgear but I wouldn't recommend using any of those these days.
For the Shadow Transcendence you can upgrade it at blacksmith NPCs in the main towns but as there is no bonus related to their upgrade levels it would be mostly pointless especially beyond the safe point of +4.
Anyway hope that helps and welcome back to IRO!