Most people in the US don't mind only having one SIM card slot on their phones. But if you absolutely need two card slots, or you're just looking for an Exynos-powered device instead of the usual Snapdragon versions sold in 'Murica, the dual-SIM Galaxy S8+ just keeps dropping in price. Now you can buy it for $629.99, about $187 off the MSRP and $36 less than the last time we reported on it.
The seller in question is 'never-msrp,' who has a 99.5% positive feedback rating, so you should feel pretty safe buying devices from them. The exact model being sold is the G955FD dual-SIM Galaxy S8+, which has an Exynos 8895 processor with 4GB of RAM and 64GB of expandable storage. Since this is an international variant, you'll want to double-check your carrier is supported, but all major GSM carriers (AT&T, T-Mobile, etc) in the US should work fine.
You can buy the S8+ from the source link below. It ships from Texas to a variety of countries worldwide.