I'd be surprised if you could still buy new synchros for these. If they're the brass type, rather than the steel "Porsche"/dog engagement type which my 56A 1:1 5-speed uses, they're same as a standard 'box.

I built my 56A 4-speed CR 'box up using the option 2 gear kit and into an old standard 'box. Also had on hand another old 'box or two and used the best of the synchros.

So far as bearings go just took any worn ones to a bearing shop and they sold me equivalent replacements.

I'm not a mechanic but with a bit of intuition and a standard workshop manual had no probs.