Just wondering if there are any maps out there because I want to improve my quick nether portal skills.

use sethbling's data pack he has nether portal building as well as many other things that would help you on a speedrun. 

https://www.youtube.com/watch?v=UihtGJhK_-w

There's one made by Twig_ that is really helpful for speed portal, MLG bucket, and blaze killing.
https://youtu.be/wTzN97UnOs0

Is there a map dedicated to practicing quick portal?

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