To dispose of Coleman propane cylinders you should check with your local landfill and see if they have a hazardous waste disposal place at the landfill.
Also some communities will have a way to dispose of hazardous waste through a trailer or a pickup day or drop off place to drop off and dispose of hazardous waste including small propane cylinders.
You could also use a hacksaw and cut open the old empty Coleman propane cylinders and then place them with some other metal to sell to a scrap metal yard.
This is what I do with them.
I don't use a lot of them but when I do have empty 1 lb propane cylinders I will cut them open with a hacksaw and place them in a 55 gallon barrel with some other scrap metal.
Then when I have enough scrap metal to sell I take it to the scrap metal yard.
Also there's an adapter you can buy that you can install on the Coleman propane cylinders and refill them with a big propane tank.
So that's another option and the propane will be cheaper that way as well.