Yes there is a Dzongkha course, but it is a full length (3CDs and a book), quite expensive course. It is by George van Driem (a Dutchmen, who spent several years researching Himalayan Languages in Bhutan. You can check online (google or yahoo) and find the link. It is usually shipped from the Netherlands. Honestly though, the Guide book such as Lonely Planet is probably your best bet as it has most of the phrases you’ll need. For your information, average Bhutanese can speak English.