Here's what fits the 50/60 series BX's for MMMs per the wholegoods catalog. Prices are from 2009 so ignore them. The number right before the price is the weight (shipinng weight?). The 48" deck is not officially offered for the 2350 or 2360, but I'm pretty sure it would fit, though it sounds like you're looking for a larger deck anyway.
MID-MOUNT MOWERS
RCK48-18BX 48 CUTTING WIDTH 250 $ 1,527.00
BX1850/60
3-Blade Finishing Mower/RH Discharge/
Shaft Drive / Quick Mount Mechanism
RCK48P18BX 48 CUTTING WIDTH 253 $ 1,639.00
BX1850/60
Fine Cut Finishing Mower /
RH Discharge / Shaft Drive /
Quick Mount Mechanism
RCK54-23BX 54 CUTTING WIDTH 282 $ 1,770.00
BX1850 /
BX1860 /
BX2350 /
BX2360 /
BX2660 /
BX24 /
BX25
3-Blade Finishing Mower / RH Discharge
Shaft Drive / Quick Mount Mechanism
RCK54P23BX 54 CUTTING WIDTH 302 $ 1,882.00
BX2350 /
BX2360 /
BX2660 /
BX24 /
BX25
Fine Cut Finishing Mower /
RH Discharge / Shaft Drive
Quick Mount Mechanism
RCK60B23BX 60 CUTTING WIDTH 317 $ 1,990.00
BX2350 /
BX2360 /
BX2660 /
BX24 /
BX25
3-Blade Finishing Mower / RH Discharge /
Shaft Drive / Quick Mount Mechanism