Candy thermometer have the wrong range if your intent is to actually measure someone's temperature.
A thermometer for human use, oral or rectal, has a range (difference between highest and lowest readings) of no more than about 8 degrees F
Approximately 97F to 105F.
OTOH, a candy thermometer has a range of at least 70F to 400F.
As a consequence, the scale of a candy thermometer, for a normal person, is far to compressed to be medically useful.
If you're just looking for a pseudo-medical toy to shove up someone's rectum, enjoy.
Glass thermometers have pretty much disappeared in the US for a couple of reasons:
Product liability lawyers suing over injuries, real or imagined
Environmental activists opposed to Mercury getting into the waste stream and it's hazards, real or imagined.
Also, the Chinese make and sell good electronic digital thermometers that are easy to read (unlike glass ones) and cost under $5