Before you do anything special, check to see if you have metal Junction boxes and metal armored cable. If so the metal cable armor and metal box functions as your safety ground.
To put in a 3 prong receptacle you should use the "grounding" type. These have a brass colored clip that grounds the receptacle tab to the screw for better connection to the metal box than a screw alone.
Are there any reliable smart plug that does not require the ground pin?
What are you looking for? A dimmer module, or switch module, in wall dimmer etc......
The ground is a safety item and though important should not effect a smart device. My house has all metal junction boxes and all my in-wall dimmers work fine. I don't have any with metal plates which I think might add a hurdle the radio could not reach.
UPDATE: My parent's home was built in 1950 (Connecticut). I changed all the 2 prong to 3 prong receptacles. A electrician friend of my dad's checked the grounds and told us it was fine/safe etc.
I was 15 at the time so I've learned a little since then.