While preparing for drafting exercises, I came across this resource. It is not exactly the same as the work we would be doing at assessment centres but I have found it useful for practising. Especially drafting the letter and memorandum exercises and it also has model answers.
This is the link if it is easier to access: http://cw.routledge.com/textbooks/9780415487153/files/Drafting_exercises.pdf
Best of Luck!
This is the link if it is easier to access: http://cw.routledge.com/textbooks/9780415487153/files/Drafting_exercises.pdf
Best of Luck!