Before I ordered the clear ones from Nomad I was going to remove the indicator from the car, remove the bulb holder from the rear of the indicator and use a Dremel drill with a small cutting wheel to cut the filter out of the indicator as mine will not just snap out as some people have done.
But have found some now for £22 delivered from Nomad but also found a guy on Ebay selling them new for about £24 delivered.
Hope this helps.