[Moto7451]

Copper is an expensive material. Its unlikely that you will find it for cheap in small quantities especially at that thickness.

Before I get started, I just wanted to point out that theres no real reason to watercool your hard drives. They don't make enough heat to justify more than a passive heatsink or a fan.

To be honest, you're probably better off getting something like 1/8" thick copper plate and drilling 1/16" holes in it for increased surface area.

4" wide, 1/8" thick copper plate - $20/ft. They will also cut it into 6" lengths as well.

You can use some UMHW for the plastic parts. Its rather inexpensive. See here.

To make threads you're going to have to buy a hand tap and different sized taps for each type of thread you want to make. Most taps will tell you what size drill bit you need for it. If you're making a 1/2" barbed block, a 1/4" NPT tap will work. You'll need to purchase at least .625" thick plastic but I'd pay the small difference for the .75" stuff. That way you'll have more room for error. Also note that with NPT barbs, for whatever reason, the measure is the radius and not the diameter (or at least it has been every time I've purchased barbs and taps, I've never found clarification on this in any case). If you're using 3/8" barbs you can get away with .5" thick material and a 3/16" NPT tap.