What are you planning to put into the ducting? Just the VM cable or other audio visual/networking cables as well?
A VM tech would install coax cable to the required length and add connectors to the cable. For fibre optic cables I think VM uses ready-made leads with the plugs already attached.
The largest diameter conduit you might get locally and easily off the shelf will be 25mm. That should certainly be able to take a single VM cable even with connectors fitted.
You may find difficulties increase if you have corners and bends in the conduit. If you are making a simple and relatively straight run you could use a continuous length of 25mm flexible conduit. If it is going under a floor, make sure it is well fixed to avoid the conduit being dragged about when the cable is pulled through. Avoid any sharp turns in the conduit. The longer the length of duct the greater the difficulty may be to pull the cable through. Fit a pull rope for the VM tech to attach the cable to.
Cable lubricant can help pull cables through ducts
https://www.screwfix.com/p/ideal-yellow-77-wire-cable-pulling-lubricant-950ml/44462
goes on as a liquid and dries to a film.