Cavendish trust have a couple that offer A levels, of which Gretton is one - parents either love it or hate it. Holmewood, Barnet is also worth a look.
Several of Priory’s schools offer A levels. Farleigh is one, there’s also Unsted Park in Surrey, Rossendale in Lancashire and North Hill House in Somerset are some of the others.
Alderwasley Hall, Nottinghamshire.
There’s also Aurora group who offers some.
Cambian have a few that do, but they have a very mixed reputation. Some hate it and there are some significant safeguarding issues, but some parents like their schools/colleges.
West Kirby school in the Wirral.
Some NAS schools offer A levels. I know Church Lawton in Cheshire, Vanguard in Lambeth and Helen Allison in Kent definitely do.
There’s a new school opening in September called Chestnut Place in Worcestershire. The proprietor is Wider Ambition who opened another well regarded school, Lokrum Fields, in Worcestershire.
Magdalen Court School in Devon.
West Heath in Kent. A SEMH school but some of their pupils have ASD.