Before you jump in to the .458 SOCOM world, be sure to check on the price and availability of ammunition.
It isn't the easiest thing to find. ...And it isn't cheap.
As for the fun side...
For upper receivers or complete rifles, stick with:
Rock River Arms
Southern Ballistic Research (SBR Ammunition)
Tromix
SSK Industries (J.D. Jones)
Only Rock River offers off-the-shelf rifles that are ready to rock and roll.
The other companies would be more of a custom build. SBR and SSK are likely to have notable wait times. Tromix has a fantastic turnaround time and great customer support, but you would need to check with them for availability.
Companies NOT on that list are using non-standard chamber dimensions that have been known to cause reliability issues with .458 SOCOM. In addition, there are multiple documented cases of the non-standard rifles, upper receivers, or barrels experiencing catastrophic failures ("blow ups") due to the incorrect dimensions.
Just this weekend, I was made aware of yet another incident involving a very well known manufacturer's .458 SOCOM rifle that blew up with factory ammo. ...Because the chamber was improperly dimensioned.
But, as long as the rifle is from one of the 'official' builders, it's a great package. I'm sure your husband would enjoy it.