I've fantasized about sleeping with a transexual for a long time and want to act on it, how does one do this?

Look in local entertainment sheets, find out where they hang out and go there. OF course they will have to want to meet you. Just because they are transexual does not mean they will just have sex with anyone.

So you will have to find one with loose morals.

If satisfying your curiosity is your only goal, your best option might be going somewhere that prostitution is legal.

If you are wanting to meet and get to know a person who you might want to get to know better and perhaps even contemplate having a relationship with, there are bars, dating sites, personal ads, etc. The same resources that are available for meeting any other human being.

Be aware that if you are looking to use someone, they may be looking to use you.