Hi Peter --
Yes, they are available, but a bit hard to find. The best place to look is on ebay. You can also take the old ones to an engineering jobber or wholesale bearing supplier in the UK and get them to match them by dimension.
I have rebuilt a number of these steering gearboxes over the years. Not that difficult. The relevant repair manual and service news (both available from
www.fillingstation.com and others) have a number of articles on how to set up the adjustment.
If you'll cover my airfare and a few nights lodging, I'll come help you do it!
All the Best,
Chip
(Longtime resident in Kenley, Surrey)