Grappling with tracking down the 'Alex Rider' graphic novels is a mood. When I wanted them, it felt like I was doing fieldwork for Scorpia. Major online book retailers are the obvious starting point – Amazon usually has the latest editions in stock, and you can often get free shipping. For a dedicated graphic novel experience, check out Book Depository; they're reliable, prices are decent, and they ship worldwide without extra fees, which is a lifesaver if you're outside the US or UK.
Independent comic shops with online stores are another fantastic route. Places like Midtown Comics or Forbidden Planet often stock them, and you're supporting a niche business. I’ve had mixed luck with Barnes & Noble's website – sometimes they have a great sale, other times it's out of stock. A tip: search for the specific titles like 'Stormbreaker: The Graphic Novel' rather than just 'Alex Rider'. The adaptations of the first few books are the most common finds; tracking down the later ones might require more patience and checking eBay or AbeBooks for second-hand copies.
I ended up getting 'Point Blanc' from a small seller on Etsy, weirdly enough, so sometimes it pays to look beyond the usual suspects. The hunt is part of the fun, honestly. My shelf looks a bit like a spy’s safehouse now.