I called Sunview (in 54suds link above), they were very helpful and sold me the rubber extrusion by the foot which arrived only a few days later.
Now, it is a b***h to get in. Instructions are to put it in hot water to make it more pliable, but these were written by someone who had never done it. It is quite a bit of work, and time consuming, to work it into the aluminum frame. Heat will be long gone before you are 1/4 done - no point. Maybe a sunny day or a heat lamp directed at it while you work would help. But that will no doubt make it shrink more.
Also, instructions suggest leaving it as long as possible, jamming the ends in to compress the overall length because it will shrink up a bit in length as it settles in. I did my best but it still shrunk away from the ends (this takes a couple of weeks). So next time I do it, I will leave maybe an inch long hanging out at each end, wait a couple of weeks, then compress it as much as possible, cut to length, and stuff the end in. Maybe there is a better way (and I haven't actually tried that one), but that's my best idea.