I have a 10 year old MTD mower. The blades will only engage when I am not over the grass. I don’t know much about mowers, but I would guess the clutch is shot and not worth replacing. I can find lots of places willing to sell me a mower, but none who will haul away the old one. The local dump doesn’t want it because of the hazardous oil and gas in it. How can I get rid of the thing?
You can try to put it in front of your house with a big “FREE” sign on it. I did that with my daughter’s old giant plastic outdoor playset this morning. When I pulled in the driveway just a little while ago, there were 3 SUV’s loading up the pieces.
If you don’t want to just set it out there, you can still advertise it as broken but free for pickup.
Have you tried scrap metal dealers?
And don’t forget to drain the oil and gas out of it first. If possible remove the tires and seat (if padded), which you can put out with your trash.
Do like George Jones and use it for trips to the liquor store. 
Remove deck and use as a 4 wheeler.
Weld a mailbox to the front/top and park it by the road. Jeff Foxworthy would like this one.
If all else fails, dig a big hole in your backyard. 
I would try Freecycle. It’s truly amazing what people will take off your hands. Disclose the condition of the mower to the best of your ability. I bet someone wll think it’s worth tinkering with.
Its possible a local school would take it (for engine repair courses).
Convert it to a racer?
Brian
Apparently you could sell it me. The one I bought two years ago is proving to be in worse condition than the one you describe. 
Tell your handiest friend, neighbor or relative “You can have it, if you can fix it.” Then grit your teeth & smile through the pain when said handy person replaces the PTO for around $100.
Or offer to do something nice for above mentioned handy person if he or she will find the damn part number so you can replace it yourself. Seriously. That is the most difficult portion of the repair. I didn’t even break a nail.