The 2 dollar bill is no longer in print or circulation. They may still be used as currency in some location, and there is no requirement to turn them in for destruction.
A simple check with the Bureau of Engraving and Printing's website will tell you that $2 bills are still in production and are still legal tender anywhere in the US. They're simply very uncommon, accounting for less than 1% of all currency in circulation. They have not been discontinued and they have not been withdrawn.
Regarding the "state $2 bill" collections, it's not necessarily a scam but neither is it a good investment. Many private companies take ordinary coins or bills and alter them in some way, then sell them at inflated prices as "instant collectibles, never to be made again" or something similar. The problem is, these are considered to be altered items by coin and note collectors, so they lose all numismatic value. There are a small number of niche-style collectors who look for gold-plated coins or overstamped bills, for example, but that's only a very narrow market.
Usually after these "collectibles" have been out for a while interest in them dries up and they are worth no more, often less, than their original selling price. In order to recoup at least some of their investment people who own them give up and spend them at face value. That's why "gold" quarters and dimes, "Lincoln-Kennedy pennies", overprinted bills, and so forth turn up in change every so often and cause a lot of confusion and misunderstanding.