Caesars Palace has $5 and $20 baccarat. Aladdin did the last time I checked (upstairs at London Club). Golden Nugget may also have new baccarat chips. I've seen a $20 on eBay that looks new.

Might be worth checking LV Hilton; they had a game with a $20 a couple of years ago. There's also a poker $20 at Bellagio.

Four Queens and Palace Station have had special use $20's in the past. You might find a few still around there.