I’ve been waiting forever
Not yet. They said 10am Pacific Time, so it should be out by now.
…then you should know.
Pack is live now. Just bought it.
As a matter of fact, yes! It is out! Just bought it! 
Looks like it’s available in the store:
Classic Helmet REQ Pack Available Now
> Description
>
> From the fields of Harvest to the mountains of Reach, Spartans have always been at the front-lines clad in Mjolnir combat armor. Unlock nine legendary helmet designs from Halo 3 and Halo: Reach to customize your Spartan in Warzone, Warzone Firefight, and Arena matches —all updated and enhanced to function with the latest Gen2 Mjolnir suits in Halo 5: Guardians. The Classic Helmet REQ Pack delivers nine helmet designs chosen from Halo’s past to outfit Spartans of today. Once unlocked*, go to Spartan Customization and select any of the new/classic helmets:• Mark V Delta – Chief tested, UNSC approved• CQB – Get up close and personal• Recon [Gen1] – Past is prologue• Military Police – Always vigilant• EOD – Boom goes the Octanitrocubane• Pilot – Aerospace dominance is always in style• Operator [Gen1] – Solving problems, Reach style• Security [Gen1] – Ever watchful for new contingencies• EVA [Gen1] – Precursor to Wrath and Ruin *For use in all game modes. Limited number of Permanent REQs available; if all have been unlocked, additional Single-Use REQs will be included. Broadband internet required (ISP fees apply); Halo 5: Guardians game and Xbox Live Gold membership (sold separately) required.
Not available in-game tho 