Apart from the BBC, are there any worthwhile companies who accept radio sitcom scripts? I think production companies are generally looking for TV only, with most radio stuff done in-house..?
Radio Ga Ga
There's plenty of them and there's masses of independently made content on Beeb radio.
Here's a complete list of all the companies the Beeb deals with.
http://www.bbc.co.uk/commissioning/radio/network/indie_slots.pdf
Celador, Above the Title, Angel Eye and The Comedy Unit are all good first ports of call. There are a load more on the list but some companies can be pretty elusive.
Lovely stuff, thanks for that ablurga