Where to find a good bicycle-trailer lighting system...in Canada
I buy all my bike lights from http://www.dealextreme.com - they are in HongKong but have free postage to Canada. 

You are just buying the same made in China stuff in the shops direct from the makers in China.  Avoid the very cheapest stuff (destined for a Dollar store near you!) and check the reviews.

edit: specifically for your trailer you can't beat this superflash from mec

edit2: Lights switching off is normally a problem with the batteries not the switch. The flashing LED lights are microprocessor controlled and a fraction of second interuption in power resets the CPU. Check the batteries are a good contact, especially rechargeables which are a tiny bit shorter than Alkalines. You might have to bend the battery clips to make a good contact.