Daughter just nabbed my stylus because she has lost all of hers! Looked for replacements online and found this. Don't know about stocks, but there were 5 at my local Argos.
Site states price valid until 7/12
Nintendo DSi Replacement Stylus Kit.
DS console game case
This replacement stylus kit for the Nintendo DSi console comes with five Nintendo DSi stylus pens and includes a strong, durable protective case to keep your Nintendo DSi console safe and sound.
* Includes a protective hard case for your DSi console and 5 spare DSi stylus.
* For ages 8 years and over.