I booked my roundtrip ticket to England, and so I'm supposed to leave on March 6. I'll be in England for 5 months. But since I'm volunteering with a charity, I need a work visa before I can get into the UK. However, the UK Border Agency has yet to send my sponsor their certificate so I can apply for my visa. So I'm trying to find Flight Cancellation/Interruption insurance that will cover me for the reason I'd be cancelling/delaying my flight (ie. government not sending documents in time). But I'm having trouble finding one that'll do this. Please help!
You may want to focus on reviewing the terms of your airline ticket to see what your option are. Most non-refundable tickets can be changed for a fee (often about $250) plus any difference in fare. If you are unable to travel on March 6th, you won't necessarily lose the full value of your ticket. Find out what the requirements are with regard to notifying the airline and/or changing the dates.
Some travel insurance companies, e.g. Travelguard, sell "cancel for any reason" coverage. But it may be more economical to follow Laura's suggestion. When you cancel a non-refundable ticket, most airlines (for the fees Laura described) will let you re-book within a year of your original booking date.