If "on order" waiting is getting you down...Unfortunately the slave cylinder and flex line do not come with the required crush washers. I re-installed the old ones and now have a slight drip, New washers on order.
If the crush washers are copper, they can be reused if they are annealed: heat them red hot (gas stove, propane torch), plunk them in a cop of water, optionally rub both faces on a sheet of 220-grit or better sandpaper. What's going on is that copper work-hardens at it compressed by the bolt, loses the ability to seal, the annealing restores it. (This does not work with aluminum crush washers).
My local NAPA (but not the O'PepVanceZone FLAPS) keeps a stash of crush washers behind the counter; Ace/TruValue hardware stores often have them back with their other hardware drawer stuff.
But these days I just keep a stash of various sizes around - bought an assortment from BelMetric many years ago, any time I'm getting low on a size I buy another half-dozen and never run out.