They are just colllars, normally chokers or martingales or resco, made of any material. They tend to be very fine and lightweight. They are made to direct the dog, not control it as that a dog can snap them easily, but most show dogs are so polite and well trained they never would.
But the purpose is for the collar to be there but not distract from the dog. I suggest gettin collars the same coor as the dog, or with a multi colored dog, the color of the neck. The collar is to fit over teh head and not leave much slack so when it tightens you don't have twenty feet of collar then leash then you.
You might find some show products through mail order pet supply companies but your best selection will be found at dog shows themselves. I show Basenjis and I use a very thin, lightweight chain collar with a 30" thin, lightweight nylon leash. You can see pics of the collars on (www.geocities.com/yodeldogs/boys.html).
Different people like different types of show collars however. In toy breeds and terriers, martingale styles seem popular. If you are able to go to a dog show, take notice of what type of collars and leads handlers of your breed are using.
You can find dog show information at www.onofrio.com and www.infodog.com
I use 1" flat black show collars, never chokers/choke chains as they are not allowed and against the rules, I don't use leather ones either just because they tend to be expensive and stretch easy not as durable as nylons.
roxy has a show collar/lead. Its very thin and its a combo of a leash the you put over the head and ajust it to fit the neck. Hers is pink anf its got a little pink braid of leather on the part that touches her neck...roxy isnt a show dog but we thought it was cute...the thing is too delicate to use for daily walking though.
hers looks like this....except the braided part isnt as thick: