RudeVC: Asking one VC for a referral to another

This happens all the time, be careful though, if you don't approach them individually you might be 'burned' to a whole group of VCs if one of them does not like you.

Also, some VCs are more open in sharing their address books than others, the general rule seems to be that VCs that are closer to the end of their funds investment cycle are much more likely to refer you if you are earlier stage.