Back in March the red iPhone 7 and iPhone 7 Pluswere announced. The color option was part of the (Product) RED charity line of products and a fresh addition to the usual gamma. Yet now after the announcement of the iPhone 8, the iPhone 8 Plus and the completely new iPhone X, the red version is no longer available for purchase.
iPhone 7 Plus (Product) Red special edition
This leaves your options limited to jet black, black, silver, gold and rose gold.
The red iPhone 7 is still listed on retailers like BestBuy and Amazon. Online shops are most likely selling whatever units they have left in stock, but chances are they won't be getting any new units.