Where can I buy radiant armor?

Excuse me, could you please elaborate on where exactly one might acquire radiant armor? I'm quite intrigued by the notion and am eager to learn more about its availability. Are there specific retailers or online marketplaces that specialize in such items? Alternatively, could it be found through more unconventional means, such as auctions or private sales? I'm hoping to gain a clearer understanding of the options available to me in my quest for radiant armor.