I bought probably 20 units of every type of seed from both the garden box and the computer, I scoured the neighborhoods, I went into all the community buildings and the park. What am I missing? Also ...
If you have City Living, use the debug cheat and buy the produce stand. Place it on your community lot of choice and then you can buy fruits and vegetables there. There is also a grocery mod that I use, do a search for it, but the debug option works quite well.