For sale is a pair of Shimano SPD-SL pedals in good condition. Look carefully at the photo to make sure these are what you want. These are not the smaller two side SPD pedals, they are the SL version. The model is Shimano PD-R550.
From Cycling News - "SPD-SL pedals, meanwhile, use a three-bolt cleat, so it's important to bear this in mind when choosing your shoes since not all shoes are compatible with both two- and three-bolt iterations. These cleats are plastic, and much larger than their off-road counterparts. Similarly, SPD-SL pedals provide a larger pedalling platform than SPD pedals, and they are often lighter and stiffer too. The entire SPD-SL pedal body is completely different from an SPD pedal, and you can only clip into one side rather than both.