In the bathroom of a recently-remodeled hotel room I found what looked like a standard light switch but it had three positions. The 'down' position turned on only a single light fixture in the bathroom. The 'up' switch turned on all lights in the bathroom. There was also a middle position which turned everything off (like the 'down' position in a normal switch).

I found this a nifty feature. When making a trip to the bathroom in the middle of the night you don't necessarily need or want bright lighting. The option to turn on only one light fixture was nice.

I would like to replace my standard light switch with one of these. Note my bathroom has only two fixtures, an overhead fluorescent fixture and a wall sconce with a compact fluorescent bulb. Does anyone know where a switch like this can be purchased?

This might be what you are looking for. Expensive though.

WallyH

It's not just the switch that has to be changed. You also have to change the conductors.

A single throw switch only has one output conductor. The three way switch has on in and two out. The two out are called travelers.

Leviton makes a Single Pole double throw switch commonly used for shutters. I have seen Maintained, and Momentary. I think for this it needs to be a Double Pole/ Double throw.
Hot will be the common on both poles then 1 light on 1 side(night light) the other half of the switch will have your bright light on both switched positions on 1 half of the switch.
This switch needs to be a "Maintained"(Not momentary). Will see if I can locate correct switch.
I'm Back, here is the Double Pole/ Double Throw switch:
Leviton White DPDT Center-OFF COMMERCIAL Decora Rocker Switch Maintained Contact 5686-2W
You can use the Single Pole/Double Throw Maintained switch if you want to use one light or the other light, and Off.
The DPDT allows Both on for bright and only the dim one at night.

Another thing I used to do with the SPDT, Center Off/ Maintained switch in the old days was when Motions didn't have the override by single pole switch. Have center for off, On is Override(direct power to light(s))Even when motion not detected, and Down/Automatic control by Motion Detector or Beam.
Another use for that switch is used with photocell, so center is off, up is on for daytime bulb changing, and down is photocell controlled. I'm glad they make it.