[Sproket]

Look at Dtekcustoms.com Rad. I have one and works nicely.
If you want dual 120mm fans on it then look at jpiperformance.com dual rad. Look at there Gallery also.
I would not go buy a used one.
Also you could try a Auto parts store but you will have to mod it to put Barbs on it.

I have a Antec 300 psu works great for me.

I cut a square in my front case and stuck the Rad out a little and use one 120mm Panaflo fan, L1A.

I bought a Relay kit for my pump but actually I just run pump 24/7 and turn off pc whenever not using it. Pond Pumps are built to run 24/7

I have the Eheim 1048, very silent and produces little heat.

Use ClearFlex tubing, I like it much better than Tygon.

Can you provide a whole pic of your inside case?