ATLAS Bipod rifle accessories have not been seen since the last two or three hotfixes. These items have stopped spawning altogether.
Whereas in other versions, these items had a relatively common spawn (up to four were found in one "visit" to Myshkino military camp) rate, in 0.60.133911 this is not the case.

After switching between both multiple private and multiple public servers, ATLAS bipods do not appear to be spawning anymore.

This issue may also be affecting the spawn of the SVD Dragunov rifles.
In 279 hours of gameplay, I have not been able to locate a single SVD while I have found several VSS Vintorez and FN FAL weapons - which to my current knowledge are arguably rarer.