They aren't extinct, they just aren't commercially viable to grow on large scales any more. A few isolated pockets of the trees survived the blight. A quick web search will turn up someone selling some if you really want to try them but like the other poster said if you've tried fake banana flavor you've tried gros michel.

if you've ever had banana laffy taffy you've had the artificially created flavor of one.

You can order them from Hawaii (or maybe you have to physically be there).

It's just no longer worth mass producing and shipping any more due to the potential to lose your entire crop.

You'd reminded me that I still wanted to try these, someday, and I went looking, again, for if there was an easier means (other than travelling to Hawaii); I found this place that delivers within the contiguous states: https://miamifruit.org/products/gros-michel-banana-box-order. If you had wanted to try one; more expensive, due to the fragility of the crop, but viable.