By mining, or digging for them along volcanic pipes which are mostly kimberlite. You have to dig and sort through a lot of rock to find the diamonds.
Diamonds can also be made in many other ways including man made but digging is still popular because the most valuable diamonds are those made by nature long ago.
You can get diamond jewellery from most jewellers and many catalogues wwith a jewellery section, there's probably somewhere you can get cut diamonds without anything attached, but I don't know the name, and if you want uncut diamonds, you need to go to somewhere where they're mined or I think they do auctions of uncut gems, so try there.
You can buy Pokemon games at many toy retailers and GameStops.
Arciest isn't a pokemon... it is Arceus. and it cannot be obtained in diamond anymore. if you have black or white, go to pokemongloballink.com to get one.
A Riolu egg can be obtained from Reiley within the Iron Island
go underground and mine until you find one
Do you mean glaceon? Glaceon can only be obtained through trade from diamond pearl or platinum.
In Eterna city after you rescue the bike shop owners Pokemon from team galactic
Piplup is obtained as a starter in Diamond and Pearl or through trades.
The only way to get a diamond is from beating dialga (diamond only) by capturing him at MT coronet.
If I'm correct, the Gracidea flower cannot be obtained in Pokemon Diamond. Sorry! (Note: The Gracidea can be obtained in Pokemon Platinum.)
Action replay is not an Pokémon item that can be obtained in Diamond.
trade it from soulsilver
From Great Marsh after you have obtained National Pokédex.
Sorry, but Entei can not be obtained in Pokemon Diamond and Pearl itself, you must transfer it from old GBA games and use the Pal park in DP to catch him.
Cyndaquil can only be obtained by migrating it, or by cheating or hacking.
You have to migrate from Sapphire or Emrald.
Put Honey on a tree
no
There is no such Pokemon as Mewthree it is a hacked Pokemon, so consequently it cannot be obtained in Pokemon Diamond.