You could use a script for that, that gives the Proof of Donation ingame to whoever fulfills some conditions or even to anyone if you want: check doc/script_commands.txt for a full guide on that and the doc/sample folder for some samples on some scripts. That amount of information may be overwhelming for a first contact, so maybe you'll prefer to read this basic scripting guide first.
You could also add it as a mob drop, either editing official mobs by editing any of the drop columns in db/pre-re or re/mob_db.txt or making your custom ones if you want.
There are more ways of getting the item ingame, such as using @item, inserting it directly into the database and so on.
