Are you looking for one of the original 700 BDL's, a Remington Classic, a Remington Custom Shop rifle, or just an action to build one of these?
Check Gun List, GunsAmerica, GunBroker, Auction Arms, etc...
You have to remember though, the reason Remington quit making rifles chambered for this cartridge is because they weren't selling well. It might be hard to pick up a used factory rifle chambered for the 8mm Mag. Any rifle chambered for a 375 H&H or 300 H&H or cartridge based on these (and left full length) could be rebarreled with an 8mm barrel and the chamber cut for the 8mm Mag.
An old Remington or Winchester PF chambered for the 375 H&H might be the cheapest route. A Douglas or Walther barrel for a couple hundred bucks, a couple hundred bucks in gunsmith costs.