a lot of those hdd 5.25 bay coolers push less than 10cfm
Since a standard 5 1/4 bay is only 41mm high, what kind of airflow did you expect from measly 40mm fans?
I guess, if noise isn't an issue you could buy a standard HD cooler with 3 x 40mm fans and replace those fans with three 10cfm Panaflos, which would theoretically give you 30cfm of airflow but at the cost of noise.
Another possible option if you're handy, would be to buy a small sheet of aluminum and make a duct. You could make the front part of the duct the same dimensions as the 5 1/4 bay and gradually, as space allows, open it up to fit an 80mm fan. That could work.
Personally, I would just find a nice area on the top or side of your case and cut a nice neat 120mm hole with a hole saw drill attachment and put in a high flow, yet relatively quiet 70CFM Adda or something.
Realistically, you just aren't going to get enough airflow out of three 40mm fans to make it worth the cost or trouble.