Her there
Samsung are indicating the SPen is no longer available from Samsung.com nor from any of their retail partners (see here
https://www.samsung.com/ie/mobile-accessories/galaxy-tab-s7-spen-black-ej-pt870bjegeu/ ) so you'll need to look at third parties.
I would strongly urge you to ensure you buy a Samsung original though and not a compatible.
I am not employed by Samsung nor do I receive any remuneration as a Samsung Members Star.
My device is an S25 Ultra.