I got my canopies via mailorder actually, as I couldn't find the riders on the website.
So go into a GW store and ask to place a mailorder using their complete list of models. You should be able to find all the harlequin models in those cataloughes - even the complete jetbike consisting of canopy/base&seat/armament/rider.
I converted mine though, seeing as I had no use for my guardian jetbikes anymore...
¤ blip ¤
actually I think I'll just give you the partnumbers. Won't that be easier?
(I just remembered I have a Citadel cataloughe from 1991. Those serialnumbers should still be valid)
"Harlequin Riders body with shuriken pistol: 071533/7"
"Harlequin Riders body with powersword: 071533/11"
"Harlequin Riders legs: : 071533/10"
"Harlequin Canopy: 071533/8"
"Saddle: 071533/3"
"Handle Bars: 071533/4"
"Shuriken cannon armament: 071533/9"
"Dual Shuriken catapult armament: 071533/5"
Hope that it will suffice. Just pray that those molds haven't been trashed ^_-
(I got my models about 1½ year ago, so hopefully they are still intact)
/Ph471