Snorunt isn’t a Pokémon introduced in generation four, but it is one of several older Pokémon that received a new evolution in Pokémon Diamond and Pearl.
Using a Dawn Stone on any female Snorunt you capture will net you a Froslass—a powerful, if frail, Ice/Ghost-type that provides Snorunt with a nice alternative evolutionary path to the physical living glacier that is Glalie.
It isn’t hard to find the Snow Hat Pokémon in Brilliant Diamond and Shining Pearl either. They are a fairly common species once you get into the northernmost areas of the Sinnoh region, specifically in the Blizzard-engulfed routes surrounding Snowpoint City.
You can encounter Snorunt naturally on Route 216, Route 217, and at the Acuity Lakefront. If you dive into the Grand Underground, you can also find Snorunt in the Whiteout Cave, Icy Cave, and Glacial Cavern Pokémon Hideaways.
You will likely be waiting a bit to capture a Snorunt considering they are mainly available around Snowpoint City, where the seventh Gym is located. You can access the Ice-type a bit earlier via the Grand Underground, starting around when you reach Celestic Town.
From there, it is as simple as grabbing a Dawn Stone from either the Icy Cave in the Grand Underground, Route 225, or Mt. Coronet so you can get yourself a Froslass. And if you still want a Glalie, then you can just level any Snorunt up to level 42.
