Sarge,
I know a few companies are looking at it. Gary Reeder just said it would be too expensive to tool up for. Wild West Guns is reportedly trying to put one together.
If you are going to a lever gun, I think a 45-70 or something of that ilk would better serve you? Wild West does chamber the .50 Alaskan in their lever guns:
Here is some data:
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BULLET POWDER GR VEL CUP
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500 S & W MAGNUM
CASE: STARLINE
BBL: 10"
PR: WINCHESTER LR
TWIST: 1:18"
TRIM: 1.615"
275 GR. BAR XPB (Starting Loads)
DIA. .500
COL: 2.085"
H4227 40.0 1891 41,000 PSI
H110 42.0 1965 43,900 PSI
LIL'GUN 40.5 1977 41,100 PSI
Longshot 20.0 1594 35,000 PSI
Titegroup 11.0 1170 22,800 PSI
275 GR. BAR XPB (Maximum Loads)
DIA. .500
COL: 2.085"
H4227 44.0 2047 48,400 PSI
H110 45.0 2082 49,300 PSI
LIL'GUN 44.0 2137 50,800 PSI
Longshot 24.5 1824 48,900 PSI
Titegroup 20.0 1707 50,300 PSI
325 GR. BAR XPB (Starting Loads)
DIA. .500
COL: 2.290"
H4227 40.0 1788 40,700 PSI
H110 42.0 1813 40,000 PSI
LIL'GUN 40.0 1862 43,700 PSI
Longshot 22.5 1599 43,300 PSI
Titegroup 12.0 1144 25,600 PSI
325 GR. BAR XPB (Maximum Loads)
DIA. .500
COL: 2.290"
H4227 43.0 1920 49,200 PSI
H110 45.3 1951 48,900 PSI
LIL'GUN 44.5 2002 49,100 PSI
Longshot 24.5 1684 49,500 PSI
Titegroup 20.0 1575 50,700 PSI
350 GR. HDY XTP (Starting Loads)
DIA. .500
COL: 1.985"
H4227 38.0 1675 41,400 PSI
H110 39.0 1712 41,500 PSI
LIL'GUN 35.0 1697 41,500 PSI
Longshot 21.0 1482 41,400 PSI
Titegroup 11.0 1032 23,100 PSI
350 GR. HDY XTP (Maximum Loads)
DIA. .500
COL: 1.985"
H4227 42.5 1863 49,900 PSI
H110 43.0 1877 50,600 PSI
LIL'GUN 42.0 1912 48,100 PSI
Longshot 23.0 1602 50,000 PSI
Titegroup 18.5 1461 50,000 PSI