Hi, Mary:
I found them on Ancestry.com. On their home page, they have data listing
next to the census record area of the page. I click on the part that says
"see all data bases," or something like that and it gives you a big list,
where the Mexican border crossing records is listed. Click on that and it
takes you to the search page. I don't know what the site address to it is
right now, because I do not get Ancestry.com, myself, but was able to use a
friend's one day and went to town for a couple of hours looking up everyone
I could that day. Good thing, because I haven't been able to use it since.
Good luck!
Corrine Ardoin
Santa Maria, California