You can find Stuart's books on various retailer sites, including:
Don't see your preferred store? You might try via Stuart's Books2Read profile.
If you are an Amazon customer, you might be interested in Kindle Unlimited, which gives you an "all you can read" service for a low monthly price. Some books by Stuart J. Whitmore may be available via Kindle Unlimited, in which case you can read them for free -- that is, at no additional cost beyond your Kindle Unlimited subscription.