The most Legitimet way to ask for a trade on the site is to post the Pokemon that you want on your profile. Make a section asking if readers have any of the following Pokemon. Then when people see you in chat they can tell you if they have any of the listed Pokemon.
Pokemon I need
Ok the other way to get someone to trade is for you to ask around on chat. People are usually happy to trade and sometimes you will find a hacker on chat. So patiences is needed to find someone that is suitable.
Maybe in the future we could have a trade centre but i doubt that.
Hope this Help ^^