If you're looking for a clamp for something 40mm in diameter, then 1.5" clamps might work (40mm = 1.57"). If you amazon search "off road clamp" you'll see some options that might work:

https://www.amazon.com/Samman-Motorcycle-Brackets-Bicycle-Mounting/dp/B092JCQ7JW/

https://www.amazon.com/AUXMART-Clamps-Mounting-Brackets-Lights/dp/B00VQ08I2A/

https://www.amazon.com/LAMPHUS-Off-Road-Horizontal-Mounting-User-Friendly/dp/B01FETT3FO/

How well they'll work is probably going to depend on how much weight they end up holding, but you could probably use two on each side. Either way, to find clamps for tubes that large, roll cage or off-road gear is where that size would be used. Exhaust as well, but most exhaust mounts aren't really much strong than regular hose clamps.

In regards to longer monitor arms, can't say I've seen many that will clear that distance. Unless maybe you look into those multi monitor stands that hold multiple monitors off to the sides. At a certain point, monitor arms need to be a lot beefier (see: expensive/complex) in order to hold the weight of a monitor further out than a foot.