even if somebody ever did find one, no one would buy it cause it would be a piece of sh!t and will just break anyway
now while I normally don't spoon feed but I'm feeling froggy I'll give it a shot tonight...
since your asking a question about cooling system plastics, I'm gonna assume that you either didn't bother to search or didn't really read too much about it...
allow me to save you some time, first off you own an LS. there are not really any companies that make aftermarket parts for this car, and the three parts that are made are terrible and will only break again in a few months. the OEM piece may be expensive but it is well made and will last you a long time (just guessing here but can i assume that you have over 100k miles on your car?) Buy Once, Cry Once.
also since you own a $40k car(even if you didn't pay anywhere near that, it doesn't change any facts), repairs will not be cheap. get used to it.
most importantly, all of the plastic parts in the cooling system have the same lifespan, you have clearly exceeded that lifespan and now you need to replace ALL of them, otherwise, you will continue to "fend" new cracks as you keep making repairs and keep replacing parts over and over until you have replaced them all anyways.