The word 'commission' implies that you are prepared to pay for the work done for you. I don't know if this the case (I assume it isn't), but people might get that idea, so just a heads up.
If this isn't the case, then I'll be brutally honest with you: it's very unlikely you'll find anyone willing to help you if yourself have no previous experience. The simply truth is that in game design, ideas are cheap: it's neither difficult nor time consuming to come up with them. Ideas, however, need time and effort to actually become content, and if the idea wasn't any good, then neither will the content be. So what you are looking for is people to turn your ideas (and generating ideas is a large part of the fun of modding to begin with) into content for you, without any compensation. Those people are extremely rare, as they may just as well choose to realise their own concepts instead (like I said, it's more fun). Furthermore, modding teams are often symbiotic: coders team up with spriters because either person lacks the skills of the other person, which they do need to successfully create a mod. If you yourself can't bring anything substantial to the table except for concepts, you're not a 'valuable' partner to other modders. So unfortunately I don't think your search will bear much fruit.
What I can advice you to do though is to look into learning how to code and/or sprite yourself: it will take some time and dedication, but it's a much more reliable way to realise your concepts, rather than to search for someone else to do it for you.
