Kit is the easiest option:

http://www.newspeedmaster.com/html/ai_removal_kit.html

I've seen reports of people using sump plugs from Nissan cars, but the kit seemed easier to me!

I bought mine from Jenks Bolts (UK based), but the one linked above looks almost identical. See here for instructions:

http://www.triumph-bonneville.com/downloads03.html