i havent seen any tabs for this before but this is how i learned to play by watching
people in pubs, so may not be entirely accurate.

verse 1:

G                     C                         
By a lonely prison wall 

G                        D
i heard a young girl calling

G                  C          D
michael they have taken you away

G                        C
for you stole trevalyans corn 

G                           D
so the young might see the morn

D                                        G  
now the prison ship lies waiting in the bay


chorus:
G   C   G
low lie the fields of athenry

G                                         D
where once we watched the small freebirds fly

G                     D     G                         D
our love was on the wing we had dreams and songs to sing

D                                     G
its so lonely round the fields of athenry


verse 2:


By a lonely prison wall 
i heard a young man calling
nothing matters mary when you're free
against the famine and the crown
i rebelled they cut me down
now you must raise our child with dignity


Chorus
chorus instrumental

verse 3:

by a lonely harbour wall 
she watched the last star falling
as the prison ship sailed out against the sky
she lived in hope and prayer
for her love in botany bay
its so lonely round the fields of athenry

chorus