If you can't find em, grind em!
The bus that I used to drive (IH 345*5) was previously driven by a woman who got fired IIRC. Despite fairly low mileage it was never quite right and was sometimes hard to get into some gears even if you double clutched properly.
One day I subbed for another driver (the bus usually stayed with the route) and her bus was just as smooth as silk to shift. It was exactly the same configuration.
I think that the driver that I replaced must have been forcing the synchros instead of coaxing it into gear
Those big old manual five speeds may have been "synchronized" 2-5 but they sure worked better if you double clutched and that was how the company trained us and expected us to drive.
One day I was driving another old bus for some reason. It was really high mileage for a school bus but it was one of my favorites to drive. I was just doing my thing in town (must have been an event in Anchorage) shifting both up and down to slow at lights, and a kid behind me asked: "mister, doesn't this bus have any brakes?"
I laughed and said yeah, it had good brakes and I was keeping them that way