Didn't you find the raid for the Pokémon you are looking for? That is not a problem! Just use the "make a wish" feature and let GO Raid Genie to make it happen.
Just let us know which raid boss you want, and we will inform our hosts to create a raid room for you.
Here how you can use "Make a Wish" feature:
Click on the "Make a Wish" button at the bottom of the main page.
If you use the feature for the time, you will be asked share a screenshot of your Pokémon GO profile for our hosts to send you raid invitations.
note
Make sure your trainer level and trainer name is visible. If your information does not seem to be correct, you can also change it manually.
Then, select the raid boss you like by tapping the button, and we will inform our hosts.
Now, the hosts are informed, and you will be notified when you are placed to a room.
When you are placed to a room, only thing you need is to go back to the main page git add -A
You can find more information about joining a raid room party from here.