Deadnettle works differently than most other herbs in the Herbalism profession in World of Warcraft: Wrath of the Lich King. There are no spawn points for Deadnettle specifically, instead it has a 35% chance to drop from three specific herbs when gathered:
Goldclover
Talandra's Rose
Tiger Lily
Where to Get Deadnettle in WotLK Classic

Since Deadnettle can only be gathered by obtaining Goldclover, Talandra's Rose, or Tiger Lily, the best places to get Deadnettle are wherever these herbs are more abundant. While there is technically a couple spawn points in other areas, we will go over which regions have the most. These three herbs show up in a variety of zones, which we will lay out here:
Zul'Drak - Talandra's Rose Only - See Talandra's Rose Farming Routes
Sholazar Basin - Goldclover, Tiger Lily
Borean Tundra - Goldclover, Tiger Lily
Howling Fjord - Goldclover, Tiger Lily
Grizzly Hills - Goldclover, Tiger Lily
We will cover all of these zones so that we are sure to answer any of your questions. We'll start with the best place to get Deadnettle, and then show alternatives if you happen to be in other regions.
Best Deadnettle Farm - Grizzly Hills
Sholazar Basin gives Grizzly Hills a run for its money, but Grizzly Hills has far more Goldclover to hit, along with numerous Tiger Lily. Farming here will mean that every herb you gather will have a 35% chance to give you Deadnettle.
There are two main Orange Routes shown in the Grizzly Hills Farming Routes below. If you choose to, you can move along the Grey Route between the two, if you'd like to merge them into one huge farming circuit to continuously traverse.
2nd Best Deadnettle Farming Guide- Sholazar Basin
Sholazar Basin is an amazing place to gather herbs when looking for Deadnettle. You will be able to get it mostly from the Tiger Lilies in this area. By following the Orange Route below, you will be able to hit a ton of Tiger Lily and some Goldclover. You will also be able to gather a massive amount of Adder's Tongue if you so choose. You can use this for other purposes or sell them on the auction house if you do not need them.
Howling Fjord Deadnettle Farming Route
In Howling Fjord, you can again focus on Tiger Lily and Goldclover. This is a less favorable region compared to the two previous, as there is a lot more space between spawn points, and elevation changes throughout the map. Nevertheless, here is the recommended pathing:
Borean Tundra Deadnettle Farm of Goldclover and Tiger Lily
The Borean Tundra farming route is really just equal to the route you take for Goldclover. As the Goldclover route continues through the center of the map where the Tiger Lilies are, this is where you would farm. The spawn points in Borean Tundra are not that close together and it tends to have less than the other zones.