Mike, you 'can' get it remapped but as you have found out it isn't common place.
If you scour the 'net' you'll find a company who can remap, but you will have to take the ECU out of it's plastic box, which certainly isn't difficult and send it to this company, I am trying to remember who or where I saw it, so you loose the use of the car for a few days. The other alternative is to add the box, which is what most of us have done. Choose your supplier!
I have a VW T5 which a brilliant vehicle but not 4wd, I couldn't afford the 4wd version and added to insult they don't do a LWB Kombi version!
So a P38 it was and at 3 grand for 1995 DSE Auto with spares prices that leave you speechless, well compared to VW et al, it does give you cheap motoring. Pair of front discs including pads for 50 quid, that won't buy you one disc for your T4!
Keep with it, once you get it sorted it will go on and on!
I bought mine to do one job of taking a mini digger on a trailer to France and I still have it, I couldn't bear to part with it! I have used it multiple times to get me from Pays de Galles (Wales) to my place in France.
The last MOT produced an amazed tester, who couldn't even find a referral, as he said it was the first time in years that has happened, there is usually something to refer! I don't believe next year I'll be as lucky as the drivers seat belts is slightly frayed.
Everything is sortable, even the air suspension!
Ian