There's a big sale on these hard luggage suitcases that clip together | Mashable
Outbound 5-Piece Softside Wheeled Travel Luggage Suitcase Set w/ Duffle, Boarding Tote & Toiletry Bags | Canadian Tire
Amazon.com | Tach V3 3-Piece Hardcase Connectable Luggage & Carryon Travel Bag Set | Rolling Suitcase with Patented Built-In Connecting System | Easily Link & Carry 9 Bags At Once (wine red)
TACH Quick-Connecting Luggage Sets (1-, 2-, or 3-, or 4-Piece) | Groupon
Vintage American Tourister (3) Piece Luggage Set (fit inside each other) Brown | eBay