I just made one last week out of 48 x 1.6mm anodized tube. I used it for the first time on Sunday at while it bowed a touch it seemed to be strong enough. I modified my old gooseneck to fit.
This place: https://www.aluminiumtc.com.au/store/category/browse/drawn_tubes/anodised/
sells it in 3m lengths already anodized.
You can buy 50mm Aluminium round section from AHPC/Goodalls which the 50mm female/male gooseneck which he sells is made to fit.
I didnt bother with an outhaul track on the new boom, and went for an outhaul system similar to this: (https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcQvjNtCWrSRnOd3ORId-YIXwzkD4GYNr9tFxYfqiYlLLXBv8W6JoDTzOJY) with a purchase system similar to the paper tiger. The line I pull for the outhaul comes through one side of a ronstan RF5 on the boom, and then the RF5 has been modified with an additional cleat and pulley to allow the mast rotation to got through the other side. I think there is a picture of a similar setup on the Mozzie Pics section.