Over the years there have been thousand of parts made by LEGO. You can find them at BrickLink and many can give you a competitive advantage. Jonathan has compiled some of the more interesting parts. There are thousands more. Happy searching!
US LETTER: 
JonathansBricklinkTips2018.pdf
UK A4: JonathansBricklinkTips2018-A4.pdf
SPANISH LETTER: JonathansBricklinkTips2018-LETTER-ES.pdf
SPANISH A4: JonathansBricklinkTips2018-A4-ES.pdf
Traducido por Antonio Zumaquero, Entrenador y Mentor FLL en España, http://roboticaliceoerasmus.es
Angela W from the Netherlands Asked: "We saw the info about the parts made by LEGO. We looked at the link for the Lego parts and it is indeed a perfect link but for teams in the Netherlands it is hard to get parts. In the Netherlands there are no shops were you can get single items only boxes with total cars etc. BRICKSHOP Holland stores have none of the items and we don't know where we can go now. Can you help us?"
Answer: You can buy these parts directly from re-sellers. Most ship internationally. All you need is a free account at BrickLink ( https://www.bricklink.com ) or BrickOwl ( http://www.brickowl.com ) and a PayPal Account (also free http://www.paypal.com)
We have ordered parts from Europe, Asia, Australia, Canada, etc. In fact many of the parts on BrickLink are not available from LEGO which is why it is fascinating. According to FLL rules you can use any official LEGO item every manufactured!