A couple of years ago I purchased a rear light that was connected to the brake cable and would light up solid or flash depending on which mode you set it to. I remember purchasing it from nashbar.com. I ended up selling the light with my bike. I am getting back into bike riding and wanted to purchase that light system again but nashbar no longer carries it. Does anyone know where I would be able to find it?

You should check out e-bike suppliers. E-bikes come with wired brake levers and kits are available to retrofit sensors to standard levers. Personally I don't want to have to deal with the wires.

1, get a hub dynamo, for power, then a headlight that runs off that ,
then you can pick up busch and muller's toplight line brake plus light
for the rear rack..

only has the wires for powering the lights are needed ,
because the Hub dynamos are Alternators, now,

the chip in the taillight senses the frequency of the power pulses,
and when they are less frequent, that indicates the bike is slowing down,
and there is more power fed from the capacitor in the taillight
to make the LED glow more brightly..

personally, with the standlight feature,
the light in back stays on when you stop. and that is good enough.

Busch & Müller Toplight Line Brake Plus
&
Busch & Müller DIWA front & rear set both offer this brake light functionality.

The Topline Brake Plus is the better of the two, allowing one to use whatever headlight one choses. DIWA is a set which must remain as a set in order to function properly.