Where can I buy AGRs?

Excuse me, I was wondering if you could provide some guidance on where I might be able to purchase AGRs? I've been hearing a lot about them lately and am interested in adding them to my portfolio, but I'm not sure where to start looking. Are there any specific exchanges or platforms that specialize in trading AGRs, or is there a more general approach I should take? Any information you could provide would be greatly appreciated.