Perhaps we need a survey of 451 tyres. I have not been short of choices. I have them from knobbly 1-3/8" to slick in 1-1/8". The racing BMX crowd have quite a good range for treaded, while for slicks there are Schwable Duranos, Panaracer Minits, Primo Comets, and I'm sure I forget a few plus not mention lots.