Psychiatry UK or ADHD 360. The wait times are long even privately. People are waiting up to a year for titration on meds.
Regardless of meds he needs strategies. ADHD UK has some useful online workshops on its website. Lots of books on Amazon with strategies. I personally found Smart But Scattered Guide for Adults very good.
Some strategies I have learned (inattentive ADHD) :
Using body doubling eg. Focus Mate. Active noise cancelling headphones. Get a coach.
Avoid negative people. Don't rush - wait half an hour and decide. Decide if you like being around crazy people or calm people - makes a big difference.
Mindset of learning from mistakes not berating yourself. Ask questions when you're not sure. If you suspect something might be a challenge - think ahead.
Use a planning template for starting a new project. Having notice boards / white boards - have a look at kan ban.
Positive self talk - people with ND encounter negative feedback. I have a book of positive quotes and quotes on my walls, framed photos. Ask 'what went well today'. Avoid energy drainers.
Have a children's timer off Amazon for procrastination.
Some kind of task management system- doesn't matter what - One Note, Planner, pen and paper - pick one and stick to it. Make sure you cannot lose your organising system- if it's on your phone, make sure you can't lose your phone - there's enough tech in existence to make your phone findable. Likewise if the issue is passwords then find one system. Pomodoro technique - 25 min bursts of organising/tidying.
Have a TILE on everything. I have them on all my keys, workpass and wallet. I don't lose them these days but I mislay them around home constantly. I have an Alexa in every room.
Make lists for everything and save them onto Google Drive etc. - every time you do something new create a list of how you did it so you can go back to it for next time.
My absolute worst trait is time management, I have no awareness - best solution is to have a daily sequence of events. Do this then this then this. Have a bucket of time for x. Know when you work well and not.
Honestly these are small things but they help a lot.
Some kind of phone blocking software app maybe useful. A mediterranean diet has been shown to have some benefit for people with ADHD. Many people use caffeine, lions mane.