Can't find a replacement SMD capacitor - markings 100 16v VD
As you gave a diameter, and only being in the ultrasonic range, I would presume it is a normal electrolytic (common black or silver cylinder capacitor), 

I am confident that you could replace it with just about any capacitor with the same or higher voltage rating and same capacitance rating (16V or higher, e.g. 35V, and 100uF) providing it still fits in the same location 

I would avoid trying to match the exact same height rather focus on a similar diameter so it mounts on the same pads.

For not much additional cost, I might suggest a "bi-polar" varient of the capacitor you choose if your not 100% sure which way it was on the PCB it was mounted, this just means it does not matter what orientation you reconnect it to the PCB, and means that its much harder for you to go wrong.

I cannot suggest a specific product due to the rules, but the common suppliers do let you sort this stuff by package size, e.g. digikey as the first supplier off the top of my head.