You've not said which device you're using to access the BBC iPlayer. Using a computer you can access all BBC radio content here:
http://www.bbc.co.uk/radio
However (very annoyingly in my view) the iPlayer app that's built into some smart TVs (and devices such as Now TV boxes) seems to have been designed by someone who thinks that radio content is unimportant (or, probably more likely, the manufacturers of those devices are simply unwilling to pay the higher licensing fees that would be needed to have a 'full' iPlayer app on them).