A quick Google suggests that it's "ombudsmen". For what it's worth, as far as I know it's also correct to use "ombudsman" when the incumbent is a woman.
I heard Jill Kerby of the Sunday Times on Newstalk this morning. She has a slight american accent and pronounces the word "ombudsmun". This works in spoken english in the plural and singular sense.
As far as I know Ombudsman is a bastardised version of a Dutch word and is not gender specific so Ombudsmen would seem to be incorrect. What the correct plural is I have no clue..... I’m very surprised and feel a little let down that Clubman doesn't know. What's going on Clubby; is there a glitch in your programme?