from the rice seed packs you can find opening packs of mystery seeds. links here
http://undeniable.info/pz/wiki/item.php?Name=HCRiceseedspacket
http://undeniable.info/pz/wiki/item.php?Name=HCMysteryseedspacket

All mystery seeds are rice or they are random, and have a chance of being rice?
Also, I can't seem to plant them?
I even have the trellis kit up, so no sow opition to sow.

When you open a mystery seeds package you get one package of random seeds, so it could take a while to find rice ...

Rice can only been grown in a planter.

But to get the planter, you need the gardening workbench, and to get that you need the gardening apron, and to get that you need linen, and the only way to get that is either pound some rice or flax. And I have spend 2 game days foraging for flax and cake up with 5 total.

There are a lot of seed but they all have an equal chance of appearing from a Mystery Seed Package. So you just might be having bad luck. Keep trying!

And Zombies drop Mystery Seed Packets so you will always have a chance to get more even if the whole map is stripped of items. Assumeing you have some sort of Zombie respawn.