I've always used cat litter. It's absorbent enough that it tends to pull the oil out of the concrete. Not sure how well it would work on a stain once it's set in for a while though, but it's cheap enough that you don't have much to lose by trying.
It's generically called a screen, and they range from a wooden frame with a section of metal mesh on it that you shovel mixed material on, which sorts itself by gravity, on up to a mechanized thing on the back of a tractor trailer with a bunch of conveyor belts to take in mixed material, then sort and distribute the various sizes.
Depending on your workforce and budget, you might be looking at a version that's somewhat like the one you shovel through, but sized for a skid-steer loader or larger front-end loader. The mechanical wonders are nice, but expensive, and I doubt your job is large enough for someone to haul one in and set it up, at least economically.
The small stuff goes through, the big stuff goes off the lower end.
Picture found at aggman.com, though it's off on some blog platform with a different address.
After you sort out the rock and level the sand, put down geotextile fabric to prevent the sand and rock from mixing before you put the rock back on top.
Since your comment implies that you'll have at this with a shovel, rather than renting machines or hiring someone with them, I'd suggest dividing the site into a grid so you can do a manageable section and then move to the next section.
Here is a much smaller skid-steer loader and a screen suited to it, that could be easily moved if somone in your area has something like it and wants to work:
Images from www.omhproscreen.com
Best Answer
If the pavers are the same on the bottom as well as the top, you can pull up the affected pavers, wash them with just water and maybe some dish soap and then put them back in upside down. The newly cleaned bottom side should match the other pavers pretty well. You'll then need to put down some sand and sweep it around to refill the joints.