I'm not really sure why they are tough to find. Not a lot of places seem to stock them even though they are pretty available periodically. Tigers, cherries, rubies, etc are the bread and butter barbs that most stick to.
Ours are an inch and a half to two inches. What they go for is variable. We've been selling them for $3.50 each, but freeing a tank by taking them all would definitely earn a big discount.