Badger ordinance makes a strong steel rail that will not gall up like aluminium will. 1-Piece Maximized Picatinny-Style 20 MOA Elevated Scope Base Remington 700 Short Action
Night force make a good one that is cheaper Nightforce One-Piece Remington 700 Short Action Steel Bases w/ 20 MOA: MSP Scope Mounts
There is another way you could do it . Add a flat standard rail first. Then buy this mount with the 20 MOA rail and 1 " inserts ( if needede ) .
MSP Variable Eye Relief Scope Mount and 30mm Rings with MOA: MSP Scope Mounts
This is another option Larue LaRue Tactical 20 MOA PSR Scope Mount QD, LT112 | LaRue Tactical
Strong mount but does not have the positioning flexibility of the MSP mount above.
The advantage is that the mount has the 20 MOA and quick release ability.
So you can remove the long range scope and the 20 MOA taper is gone and slip onto the standard rail some other sight like a Halo , Red dot or low power scope and not have the 20 MOA taper to contend with.