I don't think you'll be able to get Koni or Bilsteins as I think they are nla. But there are a range of other, lesser models out there. I'd advise against oem items and avoid Magnetti Marelli - they appear to be a good modern shock but the lower mount doesn't fit! I know, I have a pair sitting on a shelf in my garage. The Alfa Shop stock TRWs - I have their front ones on mine and they are ok. KYB as well, but have no experience of them. I'd recommend replacing the springs and bump stops while you're at it. Alternatively you could go down the coilover route - just search this Forum for details.