I'm watching Naruto Shippuden on Hulu and they only have the english dub until 140. I'm currently looking for episode 141 (Truth) in english and I can't find it any where.
Almost all the episodes from Naruto Shippuden have been dubbed into english.
The final set is set to be released on June 11 and you can check the news here.
Finally, answering "where" you can find them, You might find them on Hulu, Crunchyroll, Funimation. The reason i'm providing multiple websites is some websites are not available in other regions.