Here's what I can tell you, but the specifics of the event (dates, availability, and exact details) will be hard to confirm:
* Meloetta's Forms: The event distributed Meloetta in its Aria Form. This form is a Psychic/Normal type and learns the move "Relic Song". This form is the one you'd have received in the event.
* Distribution Method: The event was likely distributed through Nintendo Wi-Fi Connection, the method used for many Pokemon events in that era.
* Rarity: The event itself might have been a limited-time event or a more common distribution. Unfortunately, this information is not easy to find.
What's Difficult to Find:
* Exact Dates: Determining the exact event dates, specifically for the English versions, is challenging without specific event info.
* Availability: Whether this event was a single event or part of a series of events is difficult to determine.
* Specific Details: Exact information like the event code, any special requirements to access the event, or specific instructions are very hard to find.
Where to Search:
* Bulbapedia: Bulbapedia is a great resource for Pokemon information. Try searching for "Meloetta" and checking if it mentions any English distribution events.
* Serebii.net: Another great source for Pokemon information is Serebii.net. Search for "Meloetta" and look for any mention of events.
* Online Pokemon Forums: Search for online forums dedicated to Pokemon, such as the Serebii Forums or Smogon, and post a question about the event. There might be users who participated in the event and can share details.
* Old Gaming Magazines: If you have access to old gaming magazines from around the time the games were released, they might have event details.
Note: It's likely that if you have a copy of Pokemon Black or White (or both) on your Nintendo DS, you won't be able to access the event anymore. The Nintendo Wi-Fi Connection service was shut down in 2014.