Hong Kong Peak Tram & Sky Terrace 428 ticket

I have plan to go to the peak by go up by Bus from central MTR station and down by tram. I would like to go to the sky terrace too. I saw the ticket table at the official website of the peak and it also provided The Peak Tram & Sky Terrace 428 ticket [single]. Where could I buy this ticket? At the The Peak Tram Lower Terminus? Or can I buy it at the peak? Please advise.