Go ahead and type "private school grant money" in Google. You'll find top links that are broken, scams, or just out-of-date articles with their own broken links. One link looked promising, but it listed really specific grants in other places than where I live. Then there was a link to a website that wanted $90 a year to be part of their site that apparently does list what I was looking for, maybe.
The point is this: it's not that easy finding the grants, even if they do exist. And it's probably frustrating for schools and those giving out grants, since those two can't get in touch with one another without the right information being posted openly online. Really, why should someone get $90 from every school that wants a grant when the foundations offering the grants want schools to find them?
Actually, I'm sure there's a better way than searching online, and that's probably my fault for trying it, knowing what I know about people all trying to scam others using the internet. Your private school probably has a list sent to you by a reputable group not trying to make money from the deal. Maybe it's your synod or denomination or governing body. But the list is probably still not perfect, and it looks to me like that list would be very difficult to create without spending a lot of time doing so, and thus wanting to charge $90 per school to pay for the time.