Not looking for legal advice, need help paying a lawyer in the USA

[Room101isWhereIUsedtoLive]

And thought the wise women on this site might know a way of doing this.
I live in the UK but my children reside in the USA with my ex-husband.
He is using covid-19 as a means of blocking my access to them, despite what we have agreed when we divorced.
I need a lawyer to help me enforce the agreement but I am not entitled to legal aid, as I don't reside in the USA.
So has anyone got any clever ideas on finding someone who might do pro-bono?
I have tried exploring this avenue before, with no success.
Just hoping that someone here might have a suggestion for something I haven't thought of.
And please, people reading this, if you are considering a move abroad and you have children with the person you are moving with, research the Hague Convention and what it could mean for you.

When did they move?
If the children reside in the state for 6 months and are registered with the school district, Doctors, dentist etc then that is now their state
Of residence and where the court proceedings will need to happen.
If you want to change anything you need to hurry.

Thank you everyone for your advice and messages.
I will try that lawyers link.
Asking, is there somewhere you can direct me towards, that has this kind of info, that little piece of info you have given me will help me go back to one of the avenues I have already tried.
Again thank you everyone.

I didn't think there were any flights to or from the USA anyway. He can't comply of you can't fly in or they out or am I missing something?

There are flights to the US. I know somebody who just came back to the UK from the US last week.

You can fly to the US from the UK but you can't fly from the US into the EU due to a ban imposed just in the last few days