Few months back also lead slugs were available with the local dealers at Kolkata. But in recent time it seems market for these slugs have crashed as even after repeated request I could not procure the same.
These Slugs were primarily used by the air gun shooting stands at the local Fair. These slugs were sold at price of approx 120 / kilo which made it an cheap alternative for Shooting stands.
However during my recent visit to a local fair ( Just for checking what ammo they were using) revealed they were using RH pellets instead of their traditional Slugs.
Note: These slugs were intended for smoothbore AR's
There is not much resource available regarding the AR Slugs.
As per Wikipedia:
Slug: Some manufacturers also have recently introduced the more cylindrical-shaped "slug" pellets for the more powerful modern PCP air rifles. Compared to the commonly used diabolo pellets, these slug pellets resemble Minié balls and have more contact surface with the bore and hence needs greater propelling force to overcome friction, but have better aerodynamics and longer effective ranges due to the more similar shape to firearm bullets, however also require a fully rifled barrel for spin stabilization in flight.
Do share your observation incase you get a chance to sneak upon a Shooting stand at a local Fair.
Regardsdh