Well, there are a few mixed up things:
* Remington does not make the Model 70, they make the Model 700. Model 70 rifles are sold under the Winchester name.
* Remington 700s in 7mm RSAUM (Rem Short Action Ultra Mag) are not rare, but ammo for the 7mm RSAUM is going to be hard to find. Remington quit chambering the RSAUM line of cartridges about 10 years ago.
* If it is indeed a Model 70, it would be a Winchester, and it would be chambered for 7mm WSM (Winchester Short Magnum). These are not rare either.