what is a party girl?
What I know it to be is a girl who takes cocaine.
And as such, no not going to get far asking the agencies this. As they need to pretend all of their girls on their books are tea total.
Here is for example the disclaimer on Allure (I just quoted this as the other agencies don't specifically say it in their FAQ)
We cater for all tastes and desires here at Allure Escort Agency and whilst we represent a variety of escorts in all shapes and sizes, we do have a selection process. We will only represent girls who are drug free, entitled to work in the UK, girls that are reliable and who take their commitment to us as seriously as our commitment to them.
The best way to find someone would be to go onto UKE and start a reverse booking topic asking for this. Then independent and agency girls who are on there and into this would reply.
But to be honest, even there it would be kind of a leading question and one I would be surprised they would respond to.
And just so I am not mistaken. I found this old topic on UKP when someone asked what Party Girl meant
https://www.ukpunting.com/index.php?topic=10660.0