How do I use/assemble the special class items that I keep finding components for in the game. I have played the game to the end and so far the items just waste space in my inventory. It says you need access to an assembly bench, but I haven't found one. I love the game but I feel I am missing out on something because of this.

Unless you've triggered some kind of bug, then you must have passed by a lot of workbenches, before you hit the end of the game. They are occasionally (rarely, maybe one in six?) seen in missions. There doesn't seem to be any rhyme or reason where they spring up.

I think this is a pretty silly design choice. Whether you can craft should not be left up to chance and your ability to search out a workbench that will disappear after you get out of the mission.

-edit- cleaned up my grammar.

Yeah, I finally built something. I think maybe you need to go on a mission to an "xxx Facility" (not sure, though, since it's only the 2nd bench I ever found). You also have to make sure you have all 4 pieces and are bringing along the character class the items apply to (the latter of which I only found out after I arrived at the bench, so I was uselessly carting parts for a class I didn't hire). Taking 4 items along in the limited inventory for an off-chance I might be able to build something is not fun.

As to what you're missing out on: I guess you could say the accessory I built is, so far, the best accessory for that character, but it's still not so great as to think you're really missing out on anything. Only worth 50 if you sell it, so definitely not building more than once.

Pretty much this. Playing whole day and the only place with benches are the Facility ... and the accessories themselves aint nothing to write home about. ( +5% to all resist/ +10% xp/loot)