The trims can be bought from BMW, though they're costly, I'd estimate a few hundred pounds based on what I've seen on the BMW direct ebay site. You'd also need a set of trim tools to get it all off, and I'd use something like realOEM to get an idea of how it hangs together. Perhaps look at that, and also ask BMW what it would cost for them to fit it, because while it might be expensive, you know they're liable to get it right and not break anything.
e.g. a left and right of this;
http://www.ebay.co.uk/itm/BMW-Genuine-Interior-Door-Handle-Cover-Trim-Aluminium-Left-E89-Z4-51419167023-/170774612952?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item27c2f5cbd8#ht_1720wt_1413
and this;
http://www.ebay.co.uk/itm/BMW-Genuine-Centre-Console-Ashtray-Cover-Aluminium-E89-Z4-51169150275-/180808802980?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item2a190b62a4#ht_1692wt_1413
Comes to just shy of £200. I can't see the centre console part, that's likely one you'd have to speak direct with a dealer for because as far as I know, the whole centre tunnel has to come out for this to be changed. I assume you're not wanting to change the front of the dash and just the door handles/centre console?