You must be looking in the wrong place surely, or is size an issue? Two years ago the shops were full of 'wet look' 'black liquid' leggings. Topshop had lots, as did River Island (pricey) and New Look. I bought a few pairs myself . . .
Regarding the pictures newly added above: (L to R)
H&M faux leather slim trouser. Originally £16 but bought at discount. Sizing accurate, UK12 worn by model.
Primarni leggings at £6. This style were made of two different materials, which led to me having to swap/return some that were less stretchy. They came up small, and not wishing to tear them in use, I bought a size up. *Editors choice.*
M+S Limited Edition shiny leggings at £25 but they do monthly 20% discounts, so could be had at £20 if stock is available. The UK12's shown were not made correctly, but the larger size 14 were fine. (Thread did not break on the 14's even when fully stretched.) These were both the glossiest legging tested, and the most expensive. To help put the pricing into perspective; Topshop versions were originally sold for circa £20/£22, the New Look ones around £14/£16, Can't be sure, but the River Island ones would have been at least £25, and would have come up small in size. I mention the RI sizing in case anyone considers buying at auction. (Not only members read these pages.)
What the pictures can't tell you is how they felt to wear. The H&M trousers were the most constrictive, which was pleasant, and understandable given the thickness of the material. They were not sold as leggings even if they fit like a pair.
The M+S leggings were easily the more comfortable, feeling no more restrictive than tights (hose). Those shown were a 'long' and I will also road test the regular size in time. All three pairs had around an inch of length tucked up internally for the photo's.
The cheapo/imitation spanx used to maintain modesty, have a seam forward of the inside leg and a rolled edge on the hem of the legs. Both the inner seam and the leg hem were clearly visible through the Primarni and M+S leggings. Pictures that might have been used in place of those shown, have been omitted because of the seams that were visible.
All the photo's were taken on a Lumix G5 with 20mm f1.7 pancake lens. Manual focus was used, with a 10 second timer. Distance to camera was around 5-6ft which has shortened the apparent length of the models legs. Exposure was left to the camera (this time). Natural light was used, which played havoc with exposure settings, as you can see from the varying contrast levels in the photo's.