Welcome to the board! You've come to the right place to begin putting together your armor.
It all depends on what character or mando you want to put together. I would suggest using the search feature, unless you've come to a dead end on searching for an answer. But there are several makers of armor and other various pieces that would be needed.
Most people will purchase raw cast pieces, and build it up themselves, and get the pieces over a period of time, and not all at once. You can even scratch build pieces yourself if your gunho about it. If you decide to scratchbuild it, then search for "wizardofflight." He's responsible for creating a large number of diagrams/templates of armor pieces, which I have actually used myself to make armor parts.
Just search around, research, and keep checking the cargo hold for things that you may need. Good luck