What's a good bodyweight exercise for biceps Matt?
Pretty much all of them will work your biceps Tom.
All the push up movements are compund movements which use more than one muscle. A standard press up for example will work your chest, shoulders, biceps, triceps and even your abs as you use them for stability.
Unless you're looking for 18" guns then you don't need to target biceps specifically. They're only a small muscle and they plenty of work doing other exercises.
They're one of those mescles that can't help but develop pretty much in proportion with everything else.
Narrow grip pull ups are probably the closest you'll get to isolating the biceps with a bodyweight exercise from what I can think.