I used to have a B3 jacket that was treated with a coating of some sort that quickly distressed over a few months to the ideal required finish, it came with a 'swatch' of sheepskin pinned to it to show what it would look like when it had been worn a bit, and it was dead right! Mind you, it was over £300 then, 24 years ago.... Eastman Leather Clothing do a similar coating called 'Timeworn' on their A1's and '44 pattern Irvin jackets, but that one is getting towards the thick end of a grand. Check it out:
Eastman Leather Clothing - British Flight Jackets : Raf1944
I wouldn't go buying an expensive jacket and start slathering it in any leather oil/food or suchlike though, it'll only darken it and ruin the effect, like putting Cherry Blossom on a pair of Dessies....
My advice would be buy the best you possibly can and let it 'break in' naturally.