You can get Farrow & Ball in aerosols:
And F&B supply advice about non-aerosol spraying of their paints:
As well, of course, as oodles of other companies making up matching colours of varying proximity to F&B in looks!
I certainly wasn't thinking about putting a door onto trestles - rather suitably propped up and raised from the ground at the bottom. Very similarly to how a vehicle painter would tackle a Transit door.
I have most certainly found some paints simply don't want to flow out nicely by brush. Maybe judicious thinning would help? Maybe it depends on temperature, humidity, brush quality, and painter's skill? (Mine certainly is not fo the highest order.)
Possibly the best gloss finish I remember getting was by using undercoat with heavy pigment levels. Then a lacquer layer with some dye. Finally lacquer without dye. Nothing more than denibbing between coats. Far, far from perfect but very effective. And actually not much effort.