"... I can't seem to find them in any stores...."
And you won't.
That's because Henkel does not sell Somat (their brand of dishwasher products) in the USA. Your best bet would be to purchase it online from an importer - or maybe even Amazon or eBay.
Keep in mind that P&G and Reckitt-Benckiser own the US dishwasher detergent market - lock, stock, and key. Cascade and Finish have 97% of the shelf space, followed by smaller players (Colgate-Palmolive, Seventh Generation, and whatever store/private label brands are out there).
You might be wondering WHY Henkel won't bring over Somat (or a re-branded version of it)? Simple. Because P&G and R-B own so much of the market, it'd be foolish for them to try and compete. Much like how P&G dominates the laundry detergent market.
Hope this helps.