I'm on my second s-pen.

https://smile.amazon.com/Samsung-EJ-PN950BVEGUS-Galaxy-Replacement-Orchid/dp/B074G8TPY4/ref=pd_sbs_107_1/131-8601216-9666007?_encoding=UTF8&pd_rd_i=B074G8TPY4&pd_rd_r=dd5e2b44-7678-11e9-9b17-51ada22ba8a6&pd_rd_w=CJJ3O&pd_rd_wg=hjko8&pf_rd_p=588939de-d3f8-42f1-a3d8-d556eae5797d&pf_rd_r=S7N5XAS7B2XP8WKTT9M8&psc=1&refRID=S7N5XAS7B2XP8WKTT9M8

Here's the Amazon link directly from Samsung. I ordered this one for around $20 and it works perfectly. It is OEM.

Samsung EJ-PN950BVEGUS Galaxy Note8 Replacement S-Pen, Orchid Gray https://www.amazon.com/dp/B074G8TPY4/ref=cm_sw_r_cp_apa_i_UObnCbEG87B5P