BWJS - You are correct, there is a way to share out your calendar as an ICS from Exchange. To share out your own calendar, you can do the following
1) Login to OWA
2) Navigate to the Calendar
3) On the top right corner there is a link that says Share
4) You can enter either the email address of the external person you would like to share with. This will generate an email to that person and it will contain an ICS or HTML link to view the calendar or subscribe.
If you just want to generate a generic URL without sharing directly with a person you can do the following
1) Login to OWA
2) Navigate to Calendar
3) Right click on the calendar that you want to share and select Permissions
4) There is a permission that is listed as Public Link. Select the level that you want to share and save the form.
You can go back into the permissions UI to copy the HTMLor ICS link.
hope that helps and thanks for using Office 365!
David Los