from Chicago. Here's a partial list

August 1 (1746 proscription act outlawing kilts and tartan)
July 1 (1782 lifted ban on kilts and tartans)
November 30 (St. Andrew's Day - patron saint of Scotland)
January 25 (Robert Burns birthday)

And then you can add in battles such as

The battle of Stirling Bridge: Sept. 11
The battle of Bannockburn: June 24
The battle of Flodden Field: September 9
The battle of Prestonpans: September 21
The battle of Culloden: April 16th

These are only highlights (and lowlights).

But as was said above - any day is a good day to wear a kilt.