why not get a late model 5-speed or 6-speed truck transmission. Plenty out there bolted in trucks, look at the 2500's. Granted in . you may even get one from behind a 5.3 or 6.0 and get the complete driveline. 5-speed is option MW3, 6-speed is option ML6
Just got to look at 2006 or earlier as the 2007 and later have the manual trans dropped.