ISSA - International Slalom Skateboarding Association

Here's a snapshot (as of Jan 15) of what I picked up on FB. It's full of tentative dates, so maybe not fully reliable.

World Cup:

Newton's 17/2 Open Australia WC
Keeping it High 14/4 Philippines WQS
China Silk Road Challenge 21/4 China WC
Arirang Hill Fest 28/4 South Korea WQS
Festival de la Bajada 24/6 Colombia WC
King's Gate 13/7 Austria WC
Kozakov Challenge 19/7 Czech Republic WC
Verdicchio 26/7 Italy WQS
Teolo 3/8 Italy WQS
Killington Throwdown 8-10/9 United States WC

Other events:
Voss Extremuka 29-31 Norge
Transylvania Downhill 3 - 9/7 Rumania
Top Speed Challenge 16-17/9 Quebec, Canada

As a reference here's a link to the IDF website, in case you want to check the dates of their 2017 calendar before setting your own event dates.

http://internationaldownhillfederation.org/calendar/