In regards to fans...I did my nano tanks fan bank out of Princess Auto fans but have not been happy with the noise.
As far as a good replacement fan, it really depends on your room. Do you know how big the current fan is? I suspect 40mm or so but you should measure so that you can see what else is out there.
www.ncix.com is a great site for low cost computer parts. I would try there once you know what size you have already.