The best places to buy Jenever in the United States would be European grocery stores. You might also be able to find it in liquor stores.

It shares the very same origin with its English counterpart January. They all from Latin.

ianuarius --> janairo --> janero --> enero

ianuarius --> Jenever (Old North French) --> Ieneuer (13C English) --> January

Of course that depends on where you live. If you lived in Holland, you can buy it at your local liquor store. If you live in America however, it's a lot harder to get. In Oregon, McMinimans in troutdale produces an Dutch Style gin, that is fairly authentic. In the UK it's sold as Holland Gin.

The word gin derives from the Dutch word jenever and somehow winds its way back to the Latin word for juniper. Gin is made by distilling rye or other grains and flavoring it with juniper berries and other aromatics and botanicals.

Bier (dutch beer), alcoholic bitters are quite popular and every town has its own version, Jenever, the local spirit made with juniper berries and sometimes called Dutch gin, Brandewijn (a brandy-like spirit), is one of the oldest spirits and is still popular in some areas of the Netherlands, Advocaat is a thick drink, made with brandewijn, Other Dutch liqueurs include Curaçao, Triple Sec (similar to Cointreau), Parfait d'Amour, and Dutch-made versions of anisette, apricot brandy and crème de menthe.