[quote
Instead of shaving a magnesium block with a knife, what I’ve found works much better is to use the metal file on a multi-tool. It saves your knife edge, and produces shavings/dust much faster. [/quote]

Good idea.
Also, check out some of the larger gun shows in your area.

The last one I attended there was a fellow selling thin magnesium ribbons in small plastic bags. With the right container (film canister/Advil tube/etc)it would seem a great way to take the "work" out of scraping enough shavings to adequately get a fire going.