Although this may not be what you are after, some people have fabricated a diffuser by using the same material used for florecent tube lighting. You should be able to get and cut to size this diffuser material that is obtained from canadian tire or home depot. This was done by some to get clear sidemarkers but it would work for you too assuming you don't mind a clear lens versus one with an amber lens. Most provinces don't have inspections so you should be fine either way and the solution is cheap.

Tim in Calgary.