To find micro-influencers, just start messaging the ones you think would fit your brand. The fewer followers they have the less polished they usually are, so they might not even have rates or a media kit just yet. Ask them for email or message them, and inquire about partnerships and rates for what you want (post or story). And start negotiating.
You could invest in an influencer mgmt platform, I only have experience with Traackr, which I really like. Let’s you know their audience demographics and engagement rates. I also like to check to see if they’ve posted about our competitors ever before reaching out.
I’m so curious if you could recoup the price of the influencer in donations esp if you’re new or grassroots.