JPL Reffing

A&H International
The ref in the middle is typically appointed via moas, level 4 I think.

Whilst the AR and the friendlies are often a who you know thing.

If you message your local academy, you can try and get on the distros of their local refs. I've seen some on YesRef.
My youngest grandson played throughout last season in an U13 Division of the Junior Premier League.. Not in any game, home or away, as far as I am aware was an official appointed by the league. Most certainly, at every home game the official was appointed locally. In this sense my opinion of the JPL is low.
However, to be fair, there are so many Divisions spread far and wide across the country that logistically a central Ref Sec would be almost impossible to administer and regional or divisional Ref Secs impractical. (My grandsons age group had 23 different leagues/ divisions, ranging from the south coast to north Cumbria).
Suggest that you perhaps try to contact the manager of a team in the JPL, register your interest with him and see if he can provide any contact details. (The JPL website has very little information).
Hope this may be helpful.
Yup, my answer would be don't bother with the JPL
There are better teams in the County Prem Divisions and the Refs are not appointed to games
Home sides find their own officials. It's all a bit rubbish. The JPL website is terrible. Typifies the League IMO
My brother is playing JPL next season and their manager messaged me a few months back (their first season in the JPL) to ask what it’ll be like to get officials, if I know anyone who might be able to do home games, etc. It all seems very rogue and no level required to do the games.
The clubs appoint JPL directly. It's also 4x20 minutes and they want 10 minutes between quarters to justify the subs they're stealing from parents.

You're in Birmingham so get on the MJPL. £35 upto u13s, £40 u14s-u18s plus the standard is far higher.
In Birmingham there is also the option of several academies nearby. I know Wolves pay £34 for academy matches from U6 up so if you know the right people get in there. I certainly thought that was decent! I'm sure it won't be too different with Villa, Albion, Blues etc.
My lad played for a couple of seasons and can confirm it's 100% down to the clubs to source their own referees at JPL, and there's no central fee structure either so it's entirely up to them what they offer and what you're willing to accept. I'm on the rota for a couple of local teams and whilst those teams (coaches/parents/players) are good as gold, plenty aren't as they're sold the dream of little Jonny or Jane becoming a pro and being signed to an academy.
Middlesbrough use the North Riding RDO to organise its referees for matches. They tend to appoint to the CORE team.

Best starting point is your CFA's RDO.