Bergen County Camera. Pricey but they have lenses.
Edit your signature to say, "I want to buy a Canon 50/1.2 LTM lens." Post a lot. Somebody will see it.
Watch Matsuiyastore on ebay. They sometimes have the new Konica LTM lenses. The 60/1.2 has come up on occasion.
Keep in touch verbally with Precision in Austin and Houston Camera Co-op here in Houston. They get good used stuff all the time.
Long Shot: The Wolf/Ritz Camera store in north Dallas (maybe in Grapevine?) that acts as central clearing house for everything that didn't sell in other Wolf/Ritz stores. They may have used LTM lenses. Again, a verbal connection would have to be established.
Too bad you weren't in the market for LTM lenses 12-18 months ago. I remember the new Leitz LTM Summicrons in 50mm and 35mm coming up on ebay for under $1k.
Good luck!