You can download that manual
right here
from Tamiyabase. However, this is a very old (50 years!) and rare model and no one is going to have a complete gearbox or drive mechanism for this model available. You could have an open search on eBay for the next ten years and never find one. If you really want to restore it, you would have to get a second incomplete model and try to combine the parts to get one complete version. If I remember right, the gearbox is shared with (or very similar to) the one from the earlier Sherman and later Flakpanzer.
