This workers' union
http://www.hkftu.com.hk/ has discount tickets for Ocean Park. Non Member (adult) $161, (child) $84.
1-2/F., FOK SING BLDG, 234-238 SHAUKEIWAN RD., H.K.
25699622
1/F., ON FAI BLDG., 82 OLD MAIN ST., ABERDEEN, H.K.
25550322
They have another centre at 368, Lockhart Rd, 1/F Parklane Bldg.,Wanchai. 28329181
But the prices are Non-Member $165 (adult), $85 (child).
Try to find a local friend to go with you since they don't speak English, I think.
If you have a local part-time helper, you can ask her to buy them for you. Since most probably she's a member and can get member's price (more discount than this).
Disneyland doesn't have discount tickets at present.