Where can I buy runes for F2P?

I'm curious, where exactly can I acquire runes for F2P? I've been searching everywhere but haven't found a reliable source. Could you possibly point me in the right direction? I'm particularly interested in understanding the various options available and where they might be most cost-effective. Is there a specific marketplace or platform that you recommend for this purpose? Also, any tips on how to identify genuine runes and avoid fakes would be greatly appreciated. Thank you in advance for your help!