if i am getting the requirement correctly you mean to say that the calendar should have all the days (su,mo,tu,we,th,fr,sa) covering starting from 1st Sunday of April till Last Sunday of October.
You can use an extended calendar with using cycles.
Cycle definition - April till October, every year.
Extended Calendar:
1. Call Cycle that you have created above
2. Under conditions: CSun#01|CWEEK#02|CWEEK#03|CWEEK#04|CWEEK#05|CWEEK#06|CWEEK#07|CWEEK#08|CWEEK#09|CWEEK#10|CWEEK#11|CWEEK#12|CWEEK#13|CWEEK#14|CWEEK#15|CWEEK#16|CWEEK#17|CWEEK#18|CWEEK#19|CWEEK#20|CWEEK#21|CWEEK#22|CWEEK#23|CWEEK#24|CWEEK#25|CWEEK#26|CWEEK#27|CWEEK#28|CWEEK#29|CWEEK#30
i tried this at my end but results are varying dont know why. May be due to 255 character limit under condition tab, it is not giving right preview.
This is easiest that i can think of but there is more better ways to implement this scenario.
Lets hear from others.