I've been looking for one for a long time. Here's a few metal plugs I have including their weight (weighed by myself) and a link.
iTimo Metal Butt Plug Medium (348g) - https://www.amazon.co.uk/iTimo-Metal-Light-Shape-Silver/dp/B08L7S9R2F
iTimo Metal Butt Plug Large (487g) - https://www.amazon.co.uk/iTimo-Metal-Light-Shape-Silver/dp/B08L7TL7TP
Metal Butt Plug (268g) - https://www.aliexpress.com/item/4000704767032.html
NJOY Pure Plug Medium (206g) - https://www.amazon.co.uk/gp/product/B00FEKPK2O
NJOY Pure Plug Large (317g) - https://www.amazon.co.uk/gp/product/B00FEKPMDQ
NJOY Pure Plug 2.0 (573g) - https://www.amazon.co.uk/gp/product/B00FEKPQUK/
Uberkinky Juggernaut Butt Plug (1645g) - https://www.uberkinky.com/juggernaut-butt-plug-80678.html
The first three plugs are about three times as light as the remaining ones considering their size/volume so I assume they are probably made of aluminium rather than stainless steel. The Juggernaut is very big and the weight is just too much for any practical "usage". So out of these I have, the NJOY plugs are best if you want a reasonably sized plug that has a solid weight to it. I personally would prefer a more symmetrical shape, thicker stem and a different base though.
If you were asking about weighted silicone plugs (with a stainless steel weight inside), I have seen a few, but no good ones unfortunately.