I was looking at doing this, for the good of the forum - I don't need them myself, but have always wondered why no one bothered make the indicator lenses.
Due to the size and shape of the lenses you'll probably need to use a clear coat with fibre glass - I was originally considering using a silicone rubber mould, but it would need too much. Cover the lens in a releasing agent / wax and left dry - 20/30 minutes. FOr the mould my idea was to create a mould for the outside / front of the light, then once that's set, do the rears - making sure you get plenty of release agent on the mould too. When this is set drill two small holes into what will be the top of the cast, one needs to be big enough to let the resin in, the other can be very small, to let the air out - otherwise you'll have issues getting the resin in and suffer a lot of air bubbles.
The plastic for the lens... get a decent clear resin (make sure it is proper clear - most are slightly amber) and the catalyst. You'll also need to add a UV inhibitor, otherwise your clear lenses will yellow in the sunlight.
Casting... cover the mould in a releasing agent and leave to dry. Use a syringe to inject the resin into the little dimples on the inside of the lens, this just needs to be a thin layer. Once that's on, put the two halves of the cast together and "clamp" together - whatever method you use be sure that it's not too firm as to mis-shape the mould. Our in the resin and leave for the required time.
Easy really. I was going to do this out of interest really, but have too much on at the moment and this isn't necessary for me so is on the back burner. I do have the resin kit if anyone in the UK wants to give this a try.
Making the mould is a little tricky - but you can practice on anything or similar construction. Also worth practicing with the resin as you may well get air bubbles in the first couple attempts. A company called Carbon Mods sell a mould putty which makes this a lot easier, but the price goes up.
There is plenty of info on YouTube to help you with this - on Carbon Mods also.
Only other thing you need are the amber indicators from someone who's done a clear conversion.
Someone please try this! It's bugging me, but just too far down my list of jobs... non-Zed.