You can find all of the parts for the receiver and trigger assembly if you look.
Ebay has had bolts up for auction, and there is one on www.gunbroker.com now, http://www.gunbroker.com/auction/ViewItem.asp?Item=9505617
Also Brownells, and Gun Parts Corporation, will have a lot of the internal parts.
If it is a 10/22 magnum bolt you are after though be prepared to pay.
And where are you getting a Magnum aftermarket receiver?
If you buy all the parts to put a CD special together with an aftermarket steel reciever you will spend as much as a Ruger made Magnum. Might as well get the origional if the price is the same. The 10-22M allready has a steel reciever.
Just my thought on the subject. I have built a CD Special allready and love it but so far using the Ruger aluminum reciever it has cost me less than $200.
But then again half of the fun is in building your own creation, right.