I work as a relief cashier manager (glorified supervisor) at Harrah's Council Bluffs and our general rule is for guests to buy their chips at the tables. However if you mention that you are a collector and if you ask for me (or a cashier supervisor) I like to bend the rules and pull out some nice chips and sell them to collectors.

Just had a lady tonight from Salt Lake City whose brother in New York collects chips, she says she always picks up chips for him whenever she visits casinos.