make your own
I don't believe oregon aero sells patterns. You will have to make your own. Get a 27 x 34 paper pad-mine had 1" graph lines. Trace each side of each cushion and add the appropriate seam allowance. Trace the back and add seam allowance. The front is made in three pieces. Trace each section and add seam allowances.
The zippers are on the bottom and extend about 2" up each side. Get dual separating zippers to help get the cushion in more easily. If your fabric and scrim (material used on the inside of the front facing material) is extremely thick, do not use a computerized machine as it can mess with the alignment.
Kitplanes had an excellent series on upholstering aircraft cushions several years ago. Good luck.