I presume you have tried writing to all the head offices of the car dealerships to see whether they run any specifi apprenticeship schemes.
Also, has your son tried the local colleges to see whether they have any arrangements with local companies to do part-time sandwich courses?
Meanwhile, see what's on offer with your Adult Evening Classes. The brochures for the new academic year will be available now for courses started imminently. in September There may be some courses in DIY Car Maintenance which might help provide him with a little 'hands on' experience until he can find something more permanent. This way he might also make one or two valuable contacts which suggest a way forward for employment.