Welcome to the madhouse Mark.
The Schlege or fuzzy channel is available from most of the online parts suppliers like Airstream Supply, Inland RV, Out-of-Doors Mart, below is a link to one of those.
That said, I would add a couple of comments. You are at the start of a journey and take time to firstly prioritise the tasks ahead (and try to do those jobs in a way that lets you use and benefit from your coach - it will try you patience and your wallet so it needs to be your 'friend' or you will never get done!) and I would recommend taking a little time to build a relationship with the suppliers, you are going to need their help. Maybe order some small parts from each, and decide who you like doing business with; the companies above all participate in the forum, and are all good suppliers.
Also don't be afraid to move from OEM type parts - Airstream don't always get it right, and one of the benefits of taking part in the forum is to learn from others experience. In this case there are many good threads on replacing this channels in the motorhome sections (motorhome windows are different from trailer windows), although most are on replacing in the Classic motorhome which is slightly different (http://www.airforums.com/forums/f311...ce-136024.html
). If you read those threads you will see mention of an alternate channel (http://www.hitechglazing.com/product/40059/301412
) which is easier (and neater) to install - there are lots of very experienced folks on the forum and I suggest you learn from their collective experience.
This is also the case with the insert for the belt-line molding - you can order a replacement (not the same as the original orange Argosy insert but a replacement) from any of the Airstream parts suppliers, but aluminum belt-line is used extensively in the RV industry and the same replacement, in multiple colors and widths is available from many RV parts suppliers and on eBay etc. For example 50ft of insert can be bought from eBay in various colours for around $12, just measure the size you want and replace all of it so it matches.