Or a secret third option we haven't told srhutch about, the aero bumper, which is more of an acquired taste. I like it!
Most of us buy off of eBay. http://www.bmminiparts.co.uk is okay - if they don't have a price against what you want, submit a request and it's sent out to breakers. Otherwise, just check local breakers.
Where are you? Someone maybe able to recommend a bodyshop for the re-spray. Is it going to be the same colour? Actually, what've you got now? Pics would be great

These things can be quite colour specific.