Updating this because I want to add links for as many of these as I can get. Additionally, as I went back and checked the sources, I realized that this initial count was slightly mistaken and there have been more fires corroborated, so this reflects a more accurate picture. In chronological order:
Ontario, California — Kimberly-Clark Warehouse Fire, April 7th (Also I love that there's already a wiki, godspeed to the editors)
West Jefferson, Ohio — Amazon Warehouse Fire, April 8th
Newark, NJ — Chemical Warehouse Fire, April 9th
Gwinnett County, Georgia — Trash Station Fire, April 10th
Queens, NY — Lumber Yard Fire, April 11th
Brooklyn, NY — Sunset Park Warehouse Fire, April 11th
Wayne County, Ohio — Lumber Yard Fire, April 11th
Bakersfield, California — Abandoned Warehouse Fire, April 11th
Ontario, California — Ontario Mills Mall Fire, April 13th
Rahway, NJ — Lithium-ion Battery Warehouse Fire, April 13th
New Orleans, Georgia — Tesla Sales Office Fire, April 15th
Not all of these have been confirmed to be intentionally set, other causes have been officially suggested, but several of these are confirmed to be cases of arson. It's also worthwhile to note that there are strong material incentives for owners to not give publicity to the firestarters; just from getting sources for these I noticed that even searching "[state] warehouse fire" often provides results for the Kimberly-Clark blaze. The publicity is going to the one everyone already knows about; the others are not receiving the same publicity.