Freesound.org has loads of public domain sounds. There are various other similar sites too that have various royalty free sounds & creative common licensed sounds (some can be used royalty free in commercial products).
You could always seek out people on places like soundcloud if you want to hire someone to work on sound design for your game. There are plenty of people on there. Or just google sound design.
Alternatively, if you have a decent field recorder, then you could just grab your own sounds through everyday objects around you. You'd be surprised at what sounds you can record from even the least obvious items around you & in combination of two or more things around you. Want to create thunder? Clap, add a bit of reverb / delay & filter to suit. Cleaning up background noise in your recordings is also fairly simple & can be done in under 30 seconds with Audacity & the noise removal tool that comes with it. Audacity is a free audio converter & editing application for windows, mac & linux.
P.S: don't forget to check out places like reddit & indiedb.com, as people often advertise their services (sound design, music production, voice acting & so on). Some of them even offer their services for free.