wannabe-aviator
Don't be confused! Paradropping is normally a non-commercial activity (even it may seem to be commercial). You don't need to have an AOC to do paradropping flights. So private G-reg L410s can do it.
And as you said cargo is carried by non-G operated aircraft.
By the way, G-INFO database at UK CAA is not showing any G-reg L410.
Yes you can install TCAS on L410 but not RVSM. You need RVSM-capability only in RVSM airspace, and L410 will never make that high flight levels.
Caravan and Beech 1900 is no problem to operate on G-reg.