The last time I rebuilt one, these guys were able to supply all the parts I needed.
http://www.fatsco.com/index.htm It's a heavy, fairly complex transmission, but very rugged and reliable once it's built properly. Since the Hydramatic trucks had several unique details about them, swapping to a stick shift or a newer-model automatic can get challenging. Build up what you've got, and I think you'll be happier in the long run.
Jerry
