I am wondering can I add a new electrical connection for a gas range to this line?
Given that the gas range only uses electric for clock and ignition you will be fine (given 20A circuit).  Being fine and passing inspection are two different things though.

However the real question is what the oven and disposal require and the size of the circuit.  In the manual for oven and disposal there should be information about circuit requirements.   My disposal for instance says that for a 20A circuit it may be shared with one other outlet.

So read the manual to see if this will work for you.  If you gave us the exact models we could answer better.  If this is permitted work, then just ask your inspector.  Your configuration is very normal in my area but not normal in others.