We were lucky enough to get our matching
DCL t-shirts way back in '97 at WDW. They had a special section of the Emporium set-up with DCL t-shirts to promote the launch of the new cruise line. I think that was the last time they sold them at WDW. I bought them as a surprise for our three kids and wrapped them and gave them as Christmas Presents. That's how I let them know we were going to be on the Maiden Voyage of the Disney Magic!!! Too bad the Maiden Voyage cruise date got pushed back three times because of building delays. The Magic finally set sail in July of '98 and we were on her!!!!
If you call WDW Guest Merchandise, there is an option for DCL merchandise. I do not know what types of DCL merchandise is sold, but its worth the call. Maybe you could get your t-shirts before you leave. Don't forget they have an abundance of different t-shirts onboard in the shops.
the number for WDW merchandise is 407-363-6200
MJ