If it is 6.5x54 I do believe the correct nomenclature for the ammo for this would be 6.5x54 MS (as in Mannlicher-Schoenaur).
Not too many places stock ammo, or even brass for this caliber. Only place I know of is at www.ammuntions.com
. And you'll have to call him to find out what he has in stock.
Hope this helps....