For the fake leather, may I suggest this:
This is the same stuff that orgxiii.org suggests as something to use for Organization coats (but black). This is a very good site to use.
If you have the money, I say get real leather. It'll look way awesome, but most people can't spend that..
I'll go on about the rest too if you care to hear..
On the black/dark grey (can't tell which) for the bants and sleeves, you can get a catsuit on ebay in the color you want..If you like, you can cut the sleeves off of it and sew them to the white coat and make the bottom into the pants. That way you have less layers on the upper body..
As for the armor, you can use craft foam and resin. You would be making the base armor UNDER the gem looking things, abd cast the gems in blue and glue them to the foam. This would more then likely be the best looking, yet still cheaper money wise way to do it.
Gloves are obviously just leather bike gloves you can get an like walmart..But I would suggest a cycle or moterbike store.
If you have any questions on the gem things on the armor, you can hit up the forum directly under this one for props and armor. There are a lot of very smart members there that can help you a ton on that part.
Good luck with this, and I aplaud you for wanting to cosplay a Kamen Rider