Very thin walled PVC - where to get it ?

I see standard schedule 40 pipes in every home-improvement store.
But they are designed for very high pressures (450PSI for 1" pipe).

I have noticed the pipes used in commercialy available overflow
kits (like Oceanic/AllGlass MEGAFLOW) are very thin walled pipes...
For example, their 3/4" OD pipe has 0.950" ID end wall thickness
less than 0.060" - compare to:

SCH40 3/4", ID: 0.824", wall thickness: 0.113"
SCH40 1/8", wall thickness: 0.068" - you got the picture.

The bottom line is that their 3/4" pipe has a similar inside
diameter to a standard SCH40 1" pipe occupying less space
giving also much less resistance to water flow...

All is great, and I would prefer using such pipes over SCH40,
but WHERE CAN I GET SUCH THIN WALLED 1" or 3/4" PVC PIPES ?

Anybody knows?