So just wondering if anyone has a location where I can pick up a spare, I either sold it while I was zoned out, or dropped it somewhere. Any tips would great.

I think you only get 1 but I'm not sure.

Ah oh well, ive got artillery strikes anyway, who needs backup

I never have figured out what I'm supposed to do with the thing anyway. I haven't scrapped it, but it seems like wasted space.

Can't help you find a new one cause I also have no clue where to get one outside of using console commands to create a new one on PC. As for how you use it that is simple, just shoot it at the ground somewhere in the commonwealth and minutemen will come running to your aid. I tried it out when my Sanctuary settlement got attacked by raiders right after I got the flare, was kinda funny cause I shot the raider in the face with it first cause it was the weapon I had equiped at the time.