From North Ryde, just keep going down Lane Cove Rd past Rhodes and turn onto M4. If you dont mind paying toll, then go through and get off at James Ruse Dr, turn left at James Ruse Dr, turn right at Parramatta Rd until Woodville Rd. Turn left onto Woodville Rd and keep going until you get to Merrylands Rd. Turn right onto Merrylands Rd and go to the park entrance.
OR if you don't want to pay toll, get off the M4 at Silverwater Rd, turn right onto Parramatta Rd and then same directions as above.