Good morning cjw2715!
Reference your query, I have been searching for the same thing! I fitted a Blaupunkt Travelpilot DX-R 70 to my 147 last week, the sat-nav is great. Anyhow I telephoned Blaupunkt and got the following info, there is indeed an interface available from them:
Main Interface Part No. 7607587511 £52
Vehicle Specific (147) adaptor Part No. 7607621184 £10
They do not sell direct to the public, however she advised you could go into any Halfords with the above numbers and order via them.
There is a small snag (isnt there always!?)....................they are finishing a few technical bits and the parts are not due to be released for a couple of weeks.
However, I have mine on order through here www.bluespot.co.uk/install/alfa.asp
(sorry dont know how to create the link so tou will have to copy/paste!)
£47.99 for both bits inc. VAT and postage, they will desaptch as soon as they receive and not charge your card until despatched, I can reccomend them.
What head unit are you buying? Hope the info helps?