Darren, the information that has been given is correct.
There is no way that the suspension rubbers in an Al-Ko axle can be changed by anyone other than Al-Ko.
The rubbers run the full length of the axle and are put in place by a specialist machine which exerts something like 100 tons pressure to do it.
So, unless you have a couple of million to spare to buy a similar machine, it is a case of going back to Al-Ko.
It may be more cost effective to think about replacing the axle completely as that would save on carriage costs at least, just a one way carriage instead of two.
Give Al-Ko a call and ask their tech guys for advice.