CLC sells them. Look here.

Pretty much any material you can sew will be sufficient if you're just looking for sun protection.  Lightweight nylon would be my fabric of choice if I were making one, though. 

There was a guy somewhere in Eastern Shore MD that was looking to sell covers for these boats but I don't think I have his information any more.  I think he was selling them for around $200-300 if I remember correctly. 

There are lots of places selling kayak covers of all sorts if you do a quick google search for "kayak cover".  Pretty much anyplace that sells fiberglass boats will know where to source covers if you'd rather talk to a live person face to face.

FrankP

If I made or bought a nice cover to keep the sun off my kayak while I am traveling, I would probably also start to worry about sun damage to the cover, and then to the poor exposed kayak while I am paddling it.

Protecting equipment from damage makes sense only to a point. I say use it, enjoy it, and perform maintainance as required. You might be surprised, as I've been, to discover that allowing your boats to show that they have been well used makes you only love them more.

Grant

I love to use mine too.  I touch up scratches on the bottom as needed .

I store it in side out of the sun and I know I will have to strip the varnish some day and refinish that is when I will do any glass repairs.   

I just finished a thorough road test of the CLC kayak covers.  The trip was about 4,000 miles through California, Utah, Nevada, Montana, Wyoming, Idaho, Washington, & Oregon, carrying a Shearwater 17 H and a Mill Creek 16.5.  while I never use a cover for local trips up to more than 100 miles, they really paid off on this trip.  they are now spotted with squashed pugs and dirt which is not on the boats.  They are a bit of a pain to put on, which is one good reason for not using them on short hauls.  In addition to the straps provided, you need some bungies through extra edge loops provided.  You also have to leave some slack at the ends in order to get in to attach bow and stern tie-downs.  I had no objectionalbe flapping and everything held together with the exception of the attached red flag-bags.  These are lined with a rubbber substance which is exposed when the bag is inverted to become a flag.  That lining is starting to shred on both bags.  CLC has offered to replace both, but I have not decided whether that is necessary as all is still structurally sound.  I have not worried about sun exposure while traveling (both boats sat on the lakeshore for three weeks), but I think they are great for protection from road degris.  Also kept water out of the boats during violent thunder storms.

Paul

"Also kept water out of the boats during violent thunder storms."

I do agree that a little cockpit cover that fits tightly around the coaming is worthwhile to keep out rainwater. But bugs and dirt? Easy to clean.