What’s called a “Den Desk” in Animal Crossing is actually called an “Executive Desk” IRL. It’s also called a “pedestal desk” because of the appearance of the “pedestals” on the left and the right that consist of drawers that appear to hold up the writing surface on top. It’s a furniture design that became popular in the 19th and 20th centuries and is still popular today in more “classy” and, as the name suggest, “executive” office setups.
The most popular matching desk I found was this Telluride 76" Executive Desk made by Hooker Furniture. It's made of solid wood and is the spitting image of the Animal Crossing Desk. If it's not available on Amazon, you can try another furniture store like Scout & Nimble, 1 Stop Bedrooms or another furniture retailer.