The entries on the submissions calendar are from resources across the web, through email, from friends, and so forth. I am not endorsing specific publications, submission opportunities, or contests. There are some online links below, where you can find even more submission resources. There are many publications out there and many good resources to see what's happening.

Other publication submission resources on the web:

Poets & Writers
Entropy's Where to Submit 
CRWROPPS Yahoo Group
Funds for Writers Small Markets

If you have a Google/Gmail account and would like to have this information show up on your calendar, you can subscribe to it by searching for Writing Vein Salon calendar in Google calendars, or you can click on the specific submission announcement and then click on "add to my calendar."