You can look up the parts on rockauto.com, or your preferred supplier. This vehicle does have a separate resistor, as most vehicles do. It effectively has steps and controls fan speed. They burn out fairly often in most applications. By nature, resistance = heat and so they're often actually shoved into your HVAC box so air flow passes over them to help cool them.
Typically, however, a failed resistor will result in the fan only working on high. However sometimes only one or two steps will fail so I suppose you could have only the lower speeds....still on high usually it's not really using the resistor at all (full power = full speed). But I don't know exactly how this specific one is laid out.
Figure out where your blower motor is and if this happens again (ie no high speed) bang on it and see if it speeds up. Crude but potentially effective test to see if the motor is failing.
Also be sure that you're truly not getting full fan speed. It's possible a diverter door is just sending some of the flow to your feet or defrost etc, IOW the available flow is being split between destinations. If so, you've got an issue with where air is directed rather than fan speed.
