I have been progressing through the PGA tour season, 10 events in, and have notice there are 35 PGA Tour events, but only 31 listed on the calender. After checking the trophy area, there are 4 "seasonal invitationals" - spring, summer, fall, and winter.

How are these unlocked or found?

These tournaments are played on YOUR dream 18 course. You have to design your dream 18 course before you can play on it. Once you design your course, these tournaments are "unlocked".

Other tournaments throughout the year require a certain handicap or season money list ranking.

Hope this helps.

Do these tournaments appear on schedule? ie; does the Spring Invitational appear before event #8, the Players Championship at Sawgrass? If it does - do I have to wait until the next tournamant year?

Yes, they appear on the calendar page. If you have not created your Dream 18 by then, you will have to wait until next year. This will keep you from getting some of the trophy balls for the first season, but you have to play a minimum of 3 seasons to get the trophy ball that requires AT LEAST 100 tournaments anyway.

I am not sure when the first invitational is. I am almost through with the 1st season. I can check when I get home tonight.

Sorry if this is bad news. If you are early in the game you may want to start over. You could only be set back a good 15 hours of game time.