A similar question came up earlier this year with no specific answer and I posted this:-
"A few points to consider on your axle. I'm guessing it is probably an ALKO and will be foreign in origin. ALKO UK will not I believe be able to supply one so hence the concerns of your caravan service man. It would have to come from Germany, with affiliated running gear and hence be expensive. A while ago I recall mention of an axle refurb company that advertised on the C&MC magazine. Use the search facility on this site and you may find it, or look through the old magazines.
Hope this is of some use.
Colin