I bought this one from Amazon a few weeks ago. It's an OEM pen and it's, worked great.

OEM S-Pen

Here's an Amazon US link to one I bought back in September.

I haven't had any issues with it. I'd avoid off brand ones.

Ouch, how did it happen?

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Samsung's $20 replacement S-Pen: Amazon.com: Samsung EJ-PN950BBEGUS Galaxy Note8 Replacement S-Pen

Looks like on the Samsung store on Amazon it's $19.74.

edit: Amazon Warehouse Deals (returned ones) has them at $14.16 and $14.96 too. But yeah looks like those have options to have them sold and shipped by amazon.com as the seller.

https://www.amazon.com/Samsung-EJ-PN950BBEGUS-Galaxy-Note8-Replacement/dp/B074GB37V7/ref=sr_1_1?keywords=spen&qid=1558396152&s=gateway&sr=8-1-spell

I ordered from Amazon.com just last year because my clicker was wobbly.

https://www.amazon.com/gp/product/B074GB37V7/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

So far so good, just that there was no blue pen.

Here you go: Samsung EJ-PN950BBEGUS Galaxy... https://www.amazon.com/dp/B074GB37V7?ref=ppx_pop_mob_ap_share