I don't think you can get aftermarket blower coolers can you? Why do you need one, is the old one knackered? Replacement fans are available. I doubt an aftermarket blower would perform better than a stock one.
You may find a used one on the bay.
It will perform better in a small case as it will be an extra exhaust fan.
Out of curiosity, why do you want a blower / reference GPU style cooler instead of open air style?