1) Brass comes in sheet form and various shaped profiles but is more expensive and not as easy to work with as Plastruct
2) The elevator traces were cast from one taken off the Bruder Grimme potato Harvester, so not readily available anywhere
2a) The cylinders were made from Plastruct/Butyrate tubing and split pins on my harvester which worked well, car aerials also make good rams for the larger diameter ones
2b) Just use pins, wire or plastruct solid rod to fix them together
3) Just ask about, If it is Simba discs you are after I have a quantity of them in my spares box at the minute I believe. Someone on here may be able to help with other items. If not people like Walkerparts, Dave Towse and Farm Models do parts for some items
Hope that helps Sascha