You're talking about making pavement marking for a crosswalk, correct? I've seen them made and sold in O scale at York (orange hall), but haven't had luck finding you a good link to much in "O" online. Lots of HO, though. I've found "road marking" and "pavement marking" to be good search terms - but you do get a lot of chaff, as you say.
The O scale pavement markings I've seen are vinyl tape, cut to the right dimensions/spacing and ready to transfer to the "pavement". You might be able to achieve the desired effect by ordering vinyl tape, cutting it into rectangles, and placing them at even intervals. Alternatively, you might try using masking tape to create the desired crosswalk grid/template directly on the road and then hand painting in the crosswalk with white paint.
