Hi Clemence! Well, your experience was more well structured I’d say 
I normally make these things for fun, just to try out some beams, so I was not completely accurate in the methods, I must say. Also, not all the lenses are suitable to use with these LEDs.
I bought mine from AliExpress stores. Most of mine were bought in a store suggested by vwpieces, and so far I’m very pleased with them, very professional in shipping (which is paid - lenses are about 0,30€ each and shipping each type of lens is like +2€!!!). All arrived identified according to you order, inside small plastic bags.
I bought mine in different stores. Here are the links:
These are the most adequate for the S2+, as the holder can be adapted trough some cuts. They correspond to the lenses #2 and #6 above: Page Not Found - Aliexpress.com
These are other lenses used:
n.3 - https://www.aliexpress.com/item/CREE-XML-lens-With-holders-23-3mm-Smooth-surface-10-Degree-Condensing-Lens-SMD-5050/32659777715.html?spm=a2g0s.9042311.0.0.tmcTiU
n.5 (frosted) - Page Not Found - Aliexpress.com
This is one I used on this mod: Mod of old 9 led flashlight . This one I use with the holder as the host is larger! It seems the black plastic holder absorbs more the light than the white ones, that seem to reflect more.
Page Not Found - Aliexpress.com
I also bought these small lenses for some mods on the Amutorch S3 . The cilindrical holder is not adequate for those flashlights, so I had to adapt the cone holder to them to place the lenses correctly!
https://www.aliexpress.com/item/CREE-XP-E-lens-Diameter-17mm-Smooth-surface-45-Degree-LED-lens-with-stand-XPE-XPG/2048689784.html?spm=a2g0s.9042311.0.0.V09I1V
https://www.aliexpress.com/item/CREE-XP-E-XP-G-lens-Diameter-17mm-Bead-surface-60-Degree-LED-lens-with-stand/2048689105.html?spm=a2g0s.9042311.0.0.V09I1V
These optics are also pretty good in quality. The store seems to be very “recommendable” :+1: