Here's what you can try:
* Check Online Marketplaces: While unlikely to find specific "Brilliant.org for GATE CS" materials, you could try searching on platforms like eBay, OLX (depending on your region), or even Facebook groups dedicated to GATE preparation. You might find someone selling notes or summaries they created while using Brilliant.org. Be cautious and verify the seller's credibility.
* Contact GATE CS Prep Communities: Join online forums, Facebook groups, or Reddit communities dedicated to GATE CS preparation. Ask if anyone has used Brilliant.org and might be willing to share notes or resources. Many students share their own materials to help others.
* Focus on Brilliant's Free Content: Brilliant.org has a significant amount of free content. While it may not be structured specifically for the GATE exam, you can use the free resources to bolster your understanding of specific topics relevant to the syllabus.
* Consider Alternatives: Instead of searching specifically for secondhand Brilliant materials, look for secondhand copies of standard GATE CS preparation books and study materials from reputable authors and publishers. These are more readily available.
In short, directly finding used Brilliant.org materials for GATE CS is improbable. Focus on leveraging their free content and exploring alternative secondhand resources instead.