Any good model railroad shop will have lenses made by MV Lenses. They vary in size from 1mm to 1cm, in various colors.
I use their 1mm lenses for running lights on 1/350 models, and the larger ones for search lights and signal lamps.
Actually, having kids does have its benefits...my 6 year daughter came home from a birthday party with a sheet of press-on 'glitter bitz' ...basically, soft adhesive-backed rhinestones (that shows my age, huh?) in various shapes and sizes and colors...I confiscated the sheet and have been using them as well...the smallest ones work quite well for larger searchlights in 350th scale.
Jeff