The Now black boxes and sticks have been discontinued for some time.
If you want a device to watch Now on, (and other services ) then go to amazon, or Argos and buy a Roku or a Fire stick , amazon or Argos will then send you one out.
Alternately you should be able to pick one up in person from a place such as Currys
To follow up from @chilli2 NOW no longer make or sell their own devices. When you sign up to ANY streaming services it is up to you to make sure that you have a device suitable for using the app.
As for Sony, it needs to be running Android 8.0 as per this link.
Outside of that this link will explain all devices and software version needed to get the app.
All Sony Android TVs provide apps, including Now, so you would have no need to buy an extra device to get Now on one of these.
So what we need to resolve now is why you think your TV doesn’t have apps.
Firstly, what is the model number? Maybe it isn’t Android, isn’t even smart, so you will need a Roku Express or a FireStick? But tell us the model, and we can look this up for you.
Assuming it is Android, though, do you have broadband, with WiFi? If so, you can connect the TV to the internet, either over WiFi, or with a wired Ethernet cable. The instructions that came with the TV, or the interactive Help built into it, should tell you how to do this.
So proceed accordingly; and if you need more guidance, come back with that model number, and we will gladly help you further.