Not Mayfair but Son of Stag in E1 (just off Brick Lane) sell ELC gear plus other good stuff, not cheap mind you and maybe check ELC prices on line before you go if you go that is. Quite a few vintage shops around that area too, have seen the odd decent G1 and repro A2 but rare, it’s quite a trendy area these days with plenty of eateries etc.
I live in London and don't know of any but not being into bike jackets there might be, I'm just not aware but as I posted above, there's a plethora of 'vintage' shops in and around Brick Lane, E1 and some in Covent Garden - might be wise to Google it but you'll still have to foot slog the shops and search as I doubt their websites list all they have in store.
There is also the Vintage Showroom near Covent Garden. They have some nice but small collection of military jackets and leather jackets. I have been to some of those so-called vintage shops near Brick Lane and Camden, I must say I wasn't impressed at all. I think the only way to see some Aero jackets is in Scotland. There is always Lewis Leathers near the Tottenham Court Road and Rivet and Hide just round the corner. They may carry some Japanese jackets over there as well. I am not aware of anything meaning near Mayfair though.
There are two vintage shops, incl Rokit in Covent Garden on way to American Classics, which also has another vintage shop on the same street. All have leather jackets, biker and occasionally, flight. So, 4 spots to check out within 5 mins of each other.
May be worth a pop in to Rokit's warehouse if they have some jackets on the website you want to try.