I'm looking for one of those small numeric LCDs used on OTP authentication keys (the one your bank gives you to access their website, to be clear).
All LCDs I find on the various manufacturer's sites are those big 20x2 alphanumeric displays... I need something that can be fitted on a USB key. (note: it doesn't strictly have to be numeric-only, it could even be a graphical LCD for all I care...)
Since you're looking for something with only a few digits, you don't need it to have its own controller. Try looking for LCDs called "bare glass". Those are just the LCD with the segments brought out to pins or contacts intended for zebra strip connectors.
If you use one of these, you will have to drive it yourself. It's not like a LED display where each segment is turned on to display it and off to not. LCD segments are driven with AC, and must not experience any net DC. Fortunately there are various microcontrollers that have such LCD drivers built in. For example, Microchip usually puts a "9" near the end of the PIC model number to indicate the LCD driver. Once you set up the LCD driver peripheral, you get a bunch of bits in memory that you can set or clear that directly map to LCD segments being displayed or not. The 7-segment generation if you want to display numeric digits is up to you.