Having spent numerous hours trying to find a dust cover for my recently purchased SL-Q3, my problem was solved by IntoVinyl.com.
A very easy ordering process was followed up with quick despatch and good communications throughout, and although it was a little more than I really wanted to pay, I was pleasantly surprised when it arrived in about ten days.
Cover was packed extremely well with no damage what-so-ever, simple hinge assembly fixing and fitted to turntable in about 20 mins, even included adhesive buffers to cushion the lid when closing.
I added one finishing touch by tracking down a small aluminium self-adhesive "Technics Quartz" badge for the centre of lid making it appear as it would have looked when new, way back in 1978.
If you are reading this, you may have already followed the same route as I did and even considered buying a "Spares/Repairs" turntable just to get the lid!!
My advice to you would be, "Do Not Bother", save yourself a lot of time and end up with a showroom looking turntable which a brand like Technics rightfully deserves.