I've bought a bunch from Arntzen and Quality Targets and have been 100% satisfied over 1000s of hits. Last couple 2/3rds IDPA silhouettes I bought came from Bullseye Metals off of Amazon. They were only $99 per 2 and have also served well.
I have bought recently from Make It Ring targets, they are on EBay but I bought from their web site. They have free shipping and have 5/8" targets on sale cheaper than most 3/8" elsewhere.https://makeitringtargets.com/products?olsPage=t/58-ar500-steel
eBay seller kylharn is best I’ve found at reasonable prices. His 1/2” thick AR500 plates are durable.
Another recommendation for kylharn on eBay. Free shipping and low prices. They often have sales and 25% off if you order 2 or more items.
Make It Ring is having a sale on 5/8'' AR 500 targets. Just ordered three on the advice of this thread.