Where to by road flares.

Try an automotive supply or the automotive department in your local big box. Some well stocked hardware stores will have them too.

Some auto "emergency kits" come with flares too.

Police, fire, railroad expend them by the case. I got some from my late father-in-law who got a case through railroad connections.

Signal flares sold in boating supply stores or outdoor will work to.

Remember, they work for their designed purpose, signaling, in an emergency too.