No Sheep in my World

There are no sheep in my minecraft world (on survival). I used to have some but now I can't find any. (So I can't get any wool)

What I expected to happen was...:
I was expecting more sheep to spawn.

What actually happened was...:
I killed some sheep and eventually I just couldn't find anymore of them.
Steps to Reproduce:
1. Kill all sheep on world
2. Keep going until none appear anymore

Way to fix issue:
I think the best way to fix this is to make a way that can produce your own sheep.

Extra Comment:
Please help with this issue. I thought that when the new update came out, the issue would resolve but it didn't after I updated it. This is an important issue because wool is very important in the game and I can't get it without sheep. Thanks for hearing me out and hopefully you can help resolve the issue! Love the game!