Khurasan (http://khurasanminiatures.tripod.com/) – really,really cool minis but pricey if you wind up paying postage and import costs to the UK Worth the money to me, YMMV
Alternative Armies (https://www.alternative-armies.com) – extensive range of sci-fi and some useful stuff in their Sengoku range too. Where else can you get 15mm scale, armed, Japanese schoolgirls?
The Scene (https://thesceneuk.com/shop/) – small but unmissable range of Authorities and Survivors
GZG (https://shop.groundzerogames.co.uk/index.php) – more sci-fi combat oriented than cyberpunk but some useful figures and lots of useful bots, bikes, drones, etc.
Rebel Minis (http://www.rebelminis.com/) – worth it for their Black Widow mercs …. and they have much else besides!
Brigade Models (http://www.brigademodels.co.uk/) – like GZG more sci-fi combat than cyberpunk …. but …. buildings, so, so many buildings!
There are others but that should get you started …. or bankrupt 🙂
If only I’d known how much great 15mm sci-fi stuff was coming I wouldn’t be doing my sci-fi RPG games in 20mm!!!
Growing old is mandatory, growing up is entirely optional!