Are there any single logic gates which are just individual components?
Texas Instruments calls them "Little Logic". They are found in several logic families, included but not limited to 74LVC, 74AHC, and 74AUP. Other manufacturers have similar products, sometimes also available in other families e.g. NXP's 74AXP.

Note that they are strictly surface mount, as those are the most likely targets for such a device.