Does your employer supply an OWA (Outlook Web Access) option to connect to their server? If so you may be able to get your attachments this way. I'm guessing here, not telling you it will work. Try using an alternate browser like Atomic. It has more support for downloading files than Safari. And it can pretend to be a desktop browser, bypassing the mobile OWA sites.
Note: If you do bypass mobile OWA some features may not work. Mobile browsers, even when pretending to be desktop, are more limited than a full browser.
It is highly unlikely that you can get the Calendar app to support attachments.
What you may be able to do is use shared URL links to files on a server. If not your business server then another like DropBox. Even if Calendar does not support just tapping on the URLs you could copy them and then download them in an app like GoodReader.
