Google translate is your friend in this case.
Retrobike has an active Dutch contingent who are very friendly and speak perfect English. They have set up bike/parts collection network and may help you out.
Why does it have to be a Colnago? ebay has some really nice large De Rosas at the moment.
When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Actually a professional frame builder can do a much better job for about £30 since he will have the right alignment equipment, but for those of you who are a little more brave...
About a third of the way down the above linked page the process is described. I have done it once and had good results using the board technique described. Keep in mind that you are only moving the drops 2mm on each side so subtlety is the key...