Lego.com Pick a BrickLego.com Replacement Parts
https://www.lego.com/en-us/service/replacementparts
Back in January, LEGO announced that LEGO Pick a Brick and Brick & Pieces would be merged into one single platform. After some delay, the platform is now on the LEGO Shop for your shopping needs. LEGO is still monitoring for errors which you can still find here and there.
As you can see above, orders are shipped depending on if you choose Bestseller parts or Standard parts. Bestseller ones are shipped within 5 days from the Illinois warehouse ($3.50 service fee) while the Standard parts are coming straight from Denmark from 11-15 days ($7.00 service fee).
3rd Party Lego Sets and Parts