In the western diet, probably milk, yogurt and cheese are the best source for this amino acid.
Other tryptophan rich foods would be
chocolate
oats
bananas
mangoes
dried dates
sesame, sunflower or pumpkin seeds
peanuts
chickpeas
Spirulina, well known to health food shop enthusiasts, is also a good source of tryptophan, and, if you happen to travel to South East Asia, you could try durian – an indigenous fruit with a strong smell, an acquired taste for Westerners – which is also rich in tryptophan.
A normal diet should supply all the tryptophan required and there is no need to supplement it. Besides, there has been one health scare related to tryptophan in supplement form. Some research would be recommended before choosing that way.