Wrong place to ask this question: "Do not discuss means of pirating Touhou games, fan games, music, etc. that can otherwise be obtained legally."

You can buy it here, obtained from the purchasing guide

If you want any other games, you can find Touhou 15.5 and Touhou 16 on steam! Other sources such as Jbox are listed in the purchasing guide and Touhou 14 is on Playism

For acquiring the game legally, I'd say it's best to import a boxed copy from Amazon, which is thankfully not that expensive (around 22 USD at present).

You also might want to download the free demo to test the game's compatibility. It's a pretty old game, and often needs some patching to work properly on modern Windows systems.

If you don't feel like going through all that trouble (and aren't dead-set on EoSD as your first game), Double Dealing Character and Hidden Star in Four Seasons are both officially available through digital outlets.

J-List hasn't stocked it for a while, but you can still get it on Amazon.