IME DT hubs are either really easy to work on or they are totally impossible unless you have the specific tools- the rear 210 is a total non starter without the correct tool.
The 240 you mean? It’s hardly a ‘non starter’, you do need the tool to reach the bearing right in the middle of the hub shell, but because it’s right in the middle it lasts for ages. You can do all the others, including those in the freehub body with no special tools whatsoever.
You will be able to pick up the bearings needed at your local bearing supplier. It’s a bicycle wheel, it isn’t so special that the manufacturer went to the extent and expense of specifying, designing and making a particular sized bearing when the thing already exists. Which is good news for us users.
In this instance you’re right, not a given though, Tune hubs contain proprietary bearings.
Pull your end caps off OP, check what the bearings are, order 2 replacements, done. They’re very easy to work on. Could be 6802s, think 240s and 350s are.