If you read the law carefully, while one strobe might be legal (the strobes on motorcycles are not actually strobes, the are modulators), two are probably not. They can be mistaken for the pattern used by some emergency vehicles. It all depends on where you are.

When my daughter was managing a bicycle delivery company she started using them on several of the bikes. The police not only stated that they liked seeing their use but recommended that the other bike delivery companies do the same (in that city the bike delivery companies had very good relations with the police and the strobes let them know, from a distance, who the bike delivery people were for things like "otherwise illegal operation" and riding in pedestrian only areas; things that they allowed "professionals" to do but did not allow for casual riders).

That being said, I have never had any trouble, and a few compliments, from LEOs' about having a single magic-shine clone strobe on my bike. However, I have never tried two. Here in China, a fair percentage of cars and buses don't use headlights at all. The scooters seldom use them, and other than myself, and the bike club, headlights on bicycles are almost never seen.

Back to the topic at hand, I agree, try a hardware store.