You can "buy" chips by visiting a casino cage or a table game. Simply exchange cash for chips at the main cashier cage or lay cash on an empty table and ask the dealer for a "clean" chip as a keepsake.
Retailers like Spinetti's in Las Vegas specialize in real memorabilia and obsolete casino chips. Professional Sets for Home Play: where can i buy casino chips
Where you buy casino chips depends on whether you want from a real casino or professional-grade sets for a home game. Where to Buy Casino Chips Authentic Casino Souvenirs (Single Chips): You can "buy" chips by visiting a casino