It would probably help if you can tell whether the paint is latex or enamel, because a water based remover might not work well on enamel (is it high gloss?).

I looked at the Lightning Strip web site and it said they were no longer selling it. You might want to call them and find out why before you try to buy it elsewhere. Could be a health or liability issue...

Thanks!
I think the paint is latex - but we have decided not to go through the hassle of removing it. Instead, we are going to stucco over the brick. It should look really nice with our carved wood mantle and be a lot less work than trying to remove old paint.
Didn't realize they were no longer selling Lightning Strip. I was going to purchase it directly from their site.

LS is still available. Just google it & you'll find it.. Knutes sells it also. I used it on my wood stairs & it worked way better than anything else I've ever tried. I am about to purchase some more for a table I am redoing. I'd recommend it in a heartbeat.

Lightning strip is far the best of any strippers but you must be careful with it, used it for years in our restoration business. It is strong and works, but you must have heavy rubber gloves, a bucket of water near by and should have goggles as well as yours brushes, rags etc that are needed. Great product.

Where can I buy it in the United States?

You can’t buy it anymore. The manufacturer has retired, and apparently did not sell the formula