Gustaf, Congrats on the new to you Sundowner.
I have had my 1998 245 Sundowner for 3 years now and it has served me well and been trouble free. They are solid boats, and she continues to amaze me in what she can handle on the lake I boat on, where people are afraid to go out in anything under 30' on a busy weekend.
Anyway I do not know of any used canvas packages but Four Winns still supports this model which was another big factor in my purchase decision.
You can find a parts catalog here
http://www.fourwinns.net/partbook/index.php if you are interested in buying new. And if you don't have a local source for Four Winns parts since the factory does not sell direct, there is a dealer who has posted on this site here
http://www.smwebhead.com/phpBB3/viewtopic.php?f=2&t=2612&start=30 who has offered iFourWinns users a discount on parts and direct shipping. I have not used them yet, but others have and have given good comments. I do have a list working and will be contacting them soon since my "local" hour away dealer went out of business.
Also if you need any owner’s manuals, sales brochures, or spec info they are available for download here
http://www.fourwinns.com/service/past_productHope this helps.