Nowhere at any price! Obviously you are not familiar the Mannlicher-Schoenauer receiver and magazine design. On the M-S the front and rear walls and the top sides of the magazine are integral parts of the receiver forging. As such, they cannot be moved back or forth without a complete redesign of the action. The original design, models 1900 to 1911, accommodated cartridges up to 78 mm over all. This includes the M-S 6.5x54, 9x56, 8x56 and 9.5x57 aka .375 Rimless Nitro Express (hence the ".375 H&H" name for the proprietary.400/.375), as well as some others like 7x57, 8x57 and 9.3x57, .375 H&H aka .400/.375 aka .375 Velopex, not offered by Steyr, but many were rebarreled by others. 78 mm was too short for .30-06 length cartidges. So when Steyr got a contract to make .30-06 M1924 rifles for Sequoia, they redesigned the whole action. They redesigned the receiver forging so that the rear wall of the magazine was placed more to the rear of the action. This necessitated a redesign of the trigger group too and the design of a new boltstop to allow for more rearward bolt travel. Then they made a longer cartridge carrier, magazine bottom ("carrier frame" in Steyr's parlance) and magazine cover plate. This redesign resulted in the prewar 1924 and 1925 action that could take cartridges up to 85mm. The M1925 was made in .30-06, 7x64 and 8x60S only originally. The 9.3x62, 83.6 mm over all, and the 10.75x68, 81 mm, were only added to the M25 offerings during the late 1930s, hence the rarity. But the 85 mm M1925 magazine was still too short for the 1928 vintage Brenneke proprietary 9.3x64, 85.6 mm over all. So are the standard post 1950 actions, which retained the 85 mm magazine. Only when Steyr was forced by popular demand to design their "Magnum" action in 1957, they milled out the magazine as far as possible, made longer cartridge carriers and succeeded to squeeze in the 6.5x68, 8x68, both 86.5 mm, and some others like .458 Win., .257 Weatherby, .256 Win., .338 Win., all "short magnums". But they never made a factory rifle in 9.3x64. So if you want a M-S in 9.3x64, you have to find a post-1957 "Magnum" action (many 6.5x68 barrels are burned out by now), find a very good gunsmith who is able and willing to reproduce the cams on the barrel and have the thing rebarreled. But there is absolutely no chance to build a .375 H&H Magnum or a .404 on any Mannlicher-Schoenauer action.