UNLV Digital Library has some great old photos. The best thing is you can enlarge the pics. This is just one of them:

http://digital.library.unlv.edu/objects/sky/1784
I did a search for Harrah's Sports Casino but came up empty, maybe you'll have better luck?

Here's a link to discussions that were made about this particular casino (Tahoe Plaza), located in the archives of this site:
http://www.thechipboard.com/archives/archives.pl/bid/399/md/read/id/1269662/sbj/tahoe-plaza-vs-tahoe-palace/

This is the post about UNLV's Digital Library:
http://www.thechipboard.com/archives/archives.pl/bid/399/md/read/id/1269710/sbj/great-unlv-historical-casino-design-site/

If you do find a picture of Harrah's Thrifty Gambler contact Michael Petty. He would be thrilled!