I don’t know, how many visitors visit your site. At first you try to your site increasing pr 2-5 or 6, Then you take decision for add.
your rank is fine actually you may not find any ads provider directly, therefore, try to sign in on affiliate network like peerfly, ewa, cj and so on and there you will get lots of offers whose ads banner you can used on your site and you will get paid for this if visitors or sale happened through your referral link.
GetAds and Casale Media are actually really good for beginner webmasters as well. You should try reaching out them as well.
Try any publishing network their are many like chitika, infolinks, smotion media but best is google in my opinion if you want to aution an adspace for the sponser you can create an ad space too but that is not an appropriate way to earn online.
My site’s on 3rd now and its for a well known keyword. I understood your “Banana” example and Its not the case here.
See, you can contact education related website schools, colleges, nurseries etc., but one thing your services should be in same to those services. then your websites will get organic visitors. then only they will give the advertisement.