Request the transactions for the income tax account from the client?
Also does it matter for you? You're only doing the BAS and likely doing simplified BAS which requires less information: sales (G1), GST on sales (1A) and GST on expenses (1B) and if appliceable wages (W1) and PAYG withholding (W2). Generally payments to the ATO wouldn't affect the BAS figures unless it's made into another gst registered entity ATO account.