I'm not a huge fan of firelapping because it can enlarge throats, but it does have its place, especially if the throat is too small or too abrupt to begin with.
Anyway, it is easy to make your own firelapping bullets.
You'll need some abrasive compound, a scrap piece of steel flat bar, a clean file, and bullets. No special bullets are required, just use the bullets that you normally shoot. Lubed bullets work, too, perhaps even better than unlubed bullets.
Put a dab of abrasive on the steel plate, then roll the bullet back and forth a few times while pressing down lightly with the file.
Result: the bullet is now "knurled" and abrasive is embedded in the knurls. I deliberately overdid it on this bullet so the knurls would show up in the photo , normally the knurling would be very light. If the bullet has lube then abrasive will be embedded in the lube, too, which is why it's OK to use lubed bullets.
Shoot with a very light (subsonic) load. Make sure that each bullet exits the barrel, when in doubt take a peek through the barrel before firing the next shot. When you are done, give the barrel a good cleaning.
UPDATE: I now prefer to use hard bullets for firelapping. I think hard bullets do a better job of reaching the grooves whereas soft bullets tend to lap the lands, just the opposite of what you want. Also, when rolling the bullet with the file, only light pressure is required. Too much pressure on the file will make the bullet diameter undersize.