I think the man himself DLD posted a while ago that he found zinc rod for sale on Amazon. Honestly, you need about 2.5 - 3 inches of both good grade copper and very pure zinc. If either of those come in longer length, just use a metal saw and file the roughness out.
So, you have your rods; measure around your penis and testicles with a string. Find a snug but not too tight fit. That will give you the measurement of how much you want some latex or silicone hose. I suggest clear silicone hose. Buy a suitable diameter one, that will be quite tight hold when you attach the rods. Seriously, it's just attaching two rods with a piece of silicone hose, that's how simple one can say it is.
Of course one might not have a garage, the necessary tools, but overall it doesn't take a lot of tools to make a ROP.
Hope you can catch Supra, I think he has some very good quality supplies. Surely he is a busy man!
I shouldn't promise anything, but heck, maybe I should make a picture by picture of making a ROP ...