Another stab in the dark here--perhaps his remains were taken to Rio Grande City, Tx., which was just five miles away. Local cemetery records there might reveal something. Or could be that he was buried right there in Camargo. I'm not at all familiar with Mexican cemetery records, but given that Mexico was and still is predominately Catholic, and that the Church generally keeps very good records regarding such things, perhaps he was buried in the local Catholic Cemetery and maybe there is a record of it. It might be productive to contact the diocese in Camargo to see....