8mm LEDs? There are quite a few options out there. You could also buy some 8mm lenses and build an LED holder - more less a tube with the lense on the end of it. I know Axial has some larger clear lenses, used on their light kits for the rock crawlers they have. Garden Trucking sells some larger round lenses too, also clear, or orange, or red. They are larger then 5mm, I know that much, but how bit, I can't remember. Check under the company store, and then click 'lighting'.
Axial's light bucket set -
http://www3.towerhobbies.com/cgi-bin...?&I=LXYWV9&P=7
http://www3.towerhobbies.com/cgi-bin...?&I=LXYWW1&P=7
Here are some 8mm LEDs, available online.
http://www.ledssuperbright.com/8mm-led-c-8
http://ledz.com/?p=leds.8mm
Maybe this will help. I do believe you can also polish fiber optic cable and acrylic rod. Try sanding it in various grades, working your way up as fine as you can. Something like 2500 grit or even better! I've heard some guys use a business card to finish up the ends of fiber optic cables. I don't know how well it works.