"PC Desk mount" is what i searched for on amazon, and this is what i have installed here. I did not make use of any of their mounting hardware though, and i used four M6x40mm bolts with nylon locking nuts and washers straight through the desk.
VIVO monitor mounts from Amazon. This vertical one for the two in the middle: https://smile.amazon.com/gp/product/B00DGTP57A/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
And two of these for the side monitors: https://smile.amazon.com/gp/product/B00B21TLQU/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1
They make a quad-arm stand for four monitors in my exact setup, DO NOT get it. I tried it - for as well as these work, that one was equally terrible. It doesn't balance correctly and would not stand upright, the whole thing was about to come crashing down. But I've been using these VIVO stands for years and they've worked really well for me.
I got it from Amazon! I was surprised that they would deliver something so big, but they dropped it off right at my doorstep. Here's the exact one I bought: Amazon link.
I ordered it from Amazon here: https://www.amazon.com/gp/product/B087YY9ZXD/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Here you go but they're not sound absorbing.
ECHOGEAR Triple Monitor Desk Mount Stand for 3 Screens Up to 27" - Adjust Tilt, Orientation & Swivel of Each Monitor Without Tools - Lock-Down Height Adjust Eliminates Screen Wobble https://www.amazon.com/dp/B079NNC2YQ/ref=cm_sw_r_cp_api_glt_fabc_5T6DPY8NSGYYA01CBD1M?_encoding=UTF8&psc=1