Pattern crochet for lawn bowl cover?

I couldn't find what you were specifically looking for--a crocheted lawn bowl bag? Am I right? I'm not sure exactly what you were requesting, as I never found something which explained what you meant by "cover."

The best I could do, was to come up with the idea to use a crocheted bag. So, I have attached links to various free patterns.

If you are wanting something to put a single bowl into--like a ball-shaped cover for an individual bowl, I have also attached links to ball patterns. Just modify the ball shape to have a closing--something like a draw-string for the top, or a button-closure for the middle of the ball shape, to give you a couple of ideas.