You can either commission a competition for designers to build you a custom logo or you can browse the logo store to find existing logos - http://99designs.com/logo-design/store search "lawn" or "leaf" this is where I got one of my logo's.
For the competition, it's $300 but you will get over 100 submissions from designers that will create a logo based on your criteria. You can then pick the top ones you like and have them modify accordingly (my good friend just did this and it worked well)
I'd much rather look at perspective designers online portfolio and decide if they've got what it takes and commission one directly. Unfortunately, most that consider themselves designers are really awful artists.