Generally yes, you can take the unit apart if it uses a common gps module (they often do) then you may have to convert the output from 5volts to 3.3 to be safe.
My old garmin satnav uses something like this for example https://www.sparkfun.com/products/12751 sitting right under the top of the case.
Now because of the size of your units they might have the gps receiver chip/antenna/etc integrated onto one board, and in that case you are pretty much out of luck, carving up the board and trying to get the gps to work is probably not going to get you anywhere.
sparkfun and adafruit have some gps modules that you can connect power, ground, and the nmea tx serial output from the gps module to the rx serial input of the raspberry pi.
You could also go the ebay route. find a broken, sold for parts, satnav unit, then search youtube for a teardown, repeat until you find something for as cheap as you can stand that you can teardown and has a standalone module in it, THAT YOU CAN FIND docs for and can solder or otherwise wire up, some of these are a challenge (even the ones from sparkfun/adafruit/etc, get pigtails or a breakout).
Naturally start with a teardown video of the units you have and go from there.
lenik is right as well, at then end of the day $35 for a usb gps unit with a length of wire, antenna, waterproof, magnet, whatever, that in theory will just plug in and work. is not a bad option. a teardown and recycle does sound like fun though...