There are several stock photography “wants list” subscription services out there that send you daily photo requests via email. I’ve subscribed to several of them but dropped the paid one after only a year and half because the number of requests during the time I was a subscriber kept dwindling to a point where it wasn’t worth it to subscribe. During the time of my subscription, I made one calendar sale and had a few images considered for two covers. I broke even.
From what I’ve heard and seen, this used to be a common way to sell stock photos directly to new clients but almost pointless these days in my opinion since editors can find what they need online either through agencies like Alamy or on Google. So if you’re considering signing up for one of these paid services I’d suggest allocating your budget for another activity that can better get your images in front of buyers.