North American giant millipedes, native, and the practical alternative to the African species for anyone in the United States.
N. americanus reaches four inches or so and N. gordanus somewhat more. Detritivores, docile, long lived, and they will exude a defensive fluid that stains skin temporarily and is otherwise harmless. Deep substrate with rotting hardwood, same as any millipede.
Supply is almost entirely wild-collected from the eastern US, so prices are very low and availability is seasonal, thinning out through winter. Captive breeding works but nobody bothers at scale when collection is this easy, which means this market will stay accessible and stay seasonal indefinitely.