This is one of those parts that has become very hard to find and has almost no crossover to other models. Seems like it should be common considering how many LeSabres were made. See attached string from last year.
The ideal solution would be to lean on a big retailer like NAPA to have one of the original manufacturers run off a batch of a few hundred to satisfy demand for several years. There's guy in a national Plymouth club who is good at this. He samples demand among the members then convinces NAPA to stock up on an item like their early post-war water pump. When they get scarce again, he repeats the process.
What has been, can be again. (Bob Wills, 1942)