Peter Southgate wrote:
....
I wonder if anyone knows where parts can be sourced (on this occassion
bearings for the cutting deck jackshafts)

For just bearings, on this side of the pond I'd recommend pressing them
off and taking them to the local distributorship for matching.
Generally they will be a standard numbered (here Timken, or similar)
bearing and can either be supplied or crossed to another manufacturer.

If they are oddball custom, finding stuff may be really tough unless
there were enough of them that there's a collector's group or similar.
Then it becomes a case of whether it's worth the cost of trying to
machine/modify housings, etc.

--