I wrote this little headache-style OpenSCAD because I didn't have the right springs but a few ones from these:
(9 coils of 1mm wire diameter for a total lenght of 25mm with an 10mm OD and 8mm, ID)
Bearings were also an issue, the only ones I had where some scavenged from old milling cutting tools (5x9.5x3.2 or something like).
Unfortunatelly, there's quite some work after printing, check out the PDF for the details.
2x Flat Head Machine Screws are required for each spring I used M3x10mm, a little bit longer should be also ok.
For the bearing I also used another M3x10mm and due to the dimensions of those bearings I found, I also used 2x M3 washers (not to eliminate but to decrease the gap up to a minimum.
You shouldn't need the tubes/bushings/shells/whatever if you use the right bearings.
Do not force anything* or you'll end up breaking it, use the OpenSCAD (full of parameters) if something doesn't fit.
(*) The only place where force MUST carefully be done is to mount the springs.
The STL available for download are arranged in sets for 1 or 2 extruders (there's no left and right here).