adhesive glue before soldering
Honestly, it is more trouble than it's worth if you are hand soldering.  I wouldn't bother.  It is a lot of work to get the glue and part on properly, and if done improperly it will prevent you from soldering the part correctly. 

On the other hand, if you are not using glue and are using a simple hot-air soldering station, then the surface tension of the solder will align the part perfectly for you.  

Some manufacturers do use glue, but this is rare and getting more rare.  Manufacturers avoid using glue unless they absolutely have to, and glue can't be used on many PCBs.  And keep in mind that they are using glue with robots, not with hand soldering.  

As for where to buy the glue, or what glue to buy, I really don't know.  Nobody uses it by hand, so I don't know if they even make a needle point type injector for use by hand.