In Ireland, John's acquired 500 carriages (6)

'carriages' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Perhaps there's an association between them I don't understand?

'in ireland john's acquired 500' is the wordplay.
I cannot really understand how this works, but
'500' could be 'd' (Roman numeral for 500) and 'd' is located in the answer.
'in ireland john's' could be 'seans' (Irish version of the name John) and 'seans' is found in the leftover letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?