After each participation in clan war with the war battle played, you get some rewards.
What are the odds of getting any trade token?
After a recent update, your average chance is 25%. Basically, there now exists a cycle of 8 War loots, of which 2 have Trade Tokens, 1 has Gems and 5 have Gold.
If I'm not wrong, the chances for each rarity remain the same (e.g. if you get a token, there's a 40% chance to be Legendary, 30% chance to be Epic, 20% to be Rare and 10% to be Common).
According to this article and this datamine reddit post, there is a 10% chance to receive a token. The rates are broken down as follows:
Note: This could change at any time.