I have dealt with Spat and he is the only guy I would buy resin props from. Avoid ebay at all costs. Often the stuff there is cheap re-casts, poor resin mixes, or simply Spat's or Matsuo's stuff that people are trying to 'flip' by assembling them and marking them up to ridiculous prices.
"Chef" is the other armor maker with a good rep. He is based in the UK and can be easily found on the Aliens Legacy site. Where spat sells only ready-made complete sets, Chef sells his sets in 'kit form' (assembly required). Personally I think Chef's is a touch more accurate, but you do need to put in the work for assembly and deal with the exchange rate (unless you are in the UK). Chef is fast though. No long wait (which is expected since he doesn't assemble or paint it)
For what it is worth, the bottom picture you have there was made by "Golden Armor" The inaccurate trapezoid on the chest is the giveaway. They don't have a great reputation from what I have read and their armor comes in a very very labor intensive kit form. But like anything else, if you put in the work you can probably make it look good.
As for accurate accessories...hard to explain that without writing a book here in this thread! But options are out there.