The 6.5x54 Mauser is long since out of print. DWM closed down in 1972. RWS did not list it post-WW2. So the only reliable option is handloading. Cases may be formed from any standard 30-06 base brass like 6.5x57, 8x57 and so on. Use .264" 120-140 gr bullets. Remeber, the 6.5x54 Mauser cartridge was intended as a smallgame, up to roebuck number only. Standard DWM factory ballistics were a 127gr jacketed bullet at 2700 fps.