I decided to have a quick look around at where you can get spares and repairs for the QL nowadays.
For Ql repairs, try this site, called Mutant Caterpillar. It offers a QL repair service (and for other retro computers) from just under £70: https://www.mutant-caterpillar.co.uk/shop/index.php?cPath=39&sort=2a&page=2&osCsid=jf9s4qrqfc7301veh1kqv6vvg5
Or you can access it through SellMyRetro.com: https://www.sellmyretro.com/offer/details/sinclair-ql-repair-service-4065
SellMyRetro.com is always a good first port of call when searching for anything for the QL, whether it be spare parts, second hand software, peripheral cards etc.
For replacement keyboard membranes, contact RWAP Software. You can order a keyboard membrane online for £15 plus shipping costs. RWAP can supply replacement keyboard membranes for other types of retro computers too, as well as some QL spare parts. https://www.sellmyretro.com/search/naturalSearch?keyword=ql+keyboard+membrane
One QL connector which has become quite rare is the 3 pin QL power supply connection. Johan Engdahl in Sweden can supply the connectors, as well as the rubber rollers for the microdrives, via SellMyRetro.com: https://www.sellmyretro.com/user/profile/Johan/?fbclid=IwAR0UKwOZc0Fm3TFwd3NQKYAJNCP5rN9N42hI6Fj9nn5ySDwoqjI1xF6LO0Y
I’ve been told you can, with a bit of patience, adapt a molex computer fan power connector by filing away at the edges of the plug to make it fit the QL connector. Never tried this, but probably a handy tip as a last resort.
The UK-style serial and joystick connectors (Type 630W for joysticks, 631W for serial ports – these are the keyed connectors which look a little bit like British Telecom phone connectors) try Betterbox.co.uk at https://www.betterbox.co.uk/products/bt-631w-keyed-plug-ct6310.html and https://www.betterbox.co.uk/products/bt-630w.html
With 3D printers becoming ever more commonplace now, some users have taken advantage of these to print some of the hard to obtain plastic parts, such as the QL feet and expansion slot covers. Many of these designs are available to download online. Try the Yeggi search engine to find them at https://www.yeggi.com/q/sinclair+ql/ – it finds reset buttons, QL feet, expansion slot covers, even microdrive cartridge covers!
QL power supplies are like gold dust nowadays. Whether you have one which has broken, or acquired a second hand QL which came without the power supply, it’s good to know that Charley Ingley in New Zealand (who makes the vDrive units – see https://vdrivezx.com/vdriveql/) has started producing QL power adaptors, which let you plug in a traditional 12V power supply unit with a 2.1mm power connector to produce the voltages required for the QL. When available, they are sold via SellMyRetro.com. You can contact CHarley by sending a private message via the Sinclair QL FOr Everyone group on Facebook, for example, to enquire about price and availability.
And there’s always good old eBay of course – you may just strike lucky there from time to time.