You could try the Portabello road i suppose, last time i was there all sorts of vintage stuff was being flogged, though i must admit i wasn't looking for any shaving gear. That said i expect you'd pay a premium being a slightly trendy area, probably better off using ebay.
EBay EBay..Most Antique Shops in the UK & London Wont Touch Razors or Sell Em on the High Street..And..There are No Restrictions or Health & Safety Rules on Dealing with them as Some Tell Ya..As..I Asked an Antique Dealer in Glasgow..The Blood Borne Virus Scares in the 80s Scared a Lot of Folks Off Dealing in them Due to Misunderstandings of Blood Borne Viruses..
A Lot of the Dealers on EBay are Antique Dealers Of Course..Also..Its a Very Small Market..
Depending on your time, places you live/visit/work/wonder around etc.. it always worth a visit to antique and collector shops, antique and flea markets, carboot sales, charity shops. Other source can be House clearance companies(usually a self employed van driver and his mate helping him)
I did come across to shaving stuff(straight, DE and SE razors, hones, strops, shaving bowls etc..)
No harm at asking, especially if you ask nicely saying like: I collect old barber tools and shaving memorabilia... Sometimes you may get the odd looks but who cares? and as @Fergiebilly mentioned E-bay can be good but I very occasionally get lucky, usually getting outbid by 10p only seconds before the auction finishes.
Good Luck with your search and findings
I figured I could get a normal slim adjustable or black beauty with whatever I could get for this. I don't mind the way it looks too much am more interested in the functionality. Possibly open to trades, the owner said it was an unwanted gift and hasn't been used and I don't know if I am the right person for it then.
Just out of interest, how long would a razor like this last?
years and years and.... Well you know. it will last you and your son. And probably his as well. The plating may wear off but it would still be perfectly usable.
Oh and its far cooler than a slim or black beauty.