Theres a station off the SSP that sells 100oct i think its around exit 20 but not posative.
Also try SK speed for vp race fuels, they are also off the SSP but in lindenhurst/Bab area.
actually found 100 octane and 110 octane at a gas station in west hempstead, some no name place so I don't know how trustworthy they are.......and bks5 I'm not sure lol ive heard people say yes and people say no effect