Congrats on finding a trainer you like, and that you had success already. Many of us use the prong collar cause it works so well.
Did the collars look like these prongs? ( photo from http://www.leerburg.com/fit-prong.htm )
You can buy them tomorrow at many pet stores and online.
I personally prefer the smaller sized prongs for my dog than the one shown on the Doberman above. I feel I get even more control and can fit it better with the smaller links.
Here's some more sites:
Herm Sprenger Prong Collar
And from This site:
Prong W/Quick Release Snap By Herm Sprenger
Prong w/o snap
http://www.cobankopegi.com/prong.html has good background info for use of the collar.
Did the collars look like these prongs? ( photo from http://www.leerburg.com/fit-prong.htm )

You can buy them tomorrow at many pet stores and online.
I personally prefer the smaller sized prongs for my dog than the one shown on the Doberman above. I feel I get even more control and can fit it better with the smaller links.
Here's some more sites:
Herm Sprenger Prong Collar
And from This site:
Prong W/Quick Release Snap By Herm Sprenger
Prong w/o snap
http://www.cobankopegi.com/prong.html has good background info for use of the collar.