The mIRC website does not host user scripts for download. People are encouraged to write their own mIRC client scripts.
You are expressly discouraged from installing scripts that you did not write yourself, or in which you do not fully comprehend each and every line there written. mIRC scripts are fully capable of stealing and destroying data on your computer.
If you wish to find some mIRC scripts where you can learn by example, they are easily located on web search engines like Google.