ThE keys are easily available... But all they do is unground the ignition. Assuming your impromptu key is doing that...
There's no fuel valve left unopened?
Probably clogged carb from dried varnished gas... Empty isn't completely empty,
You may have luck with a teaspoon or 2 down the plug hole, then try to start. Should at least run a moment. Also proves the ignition.
If so, clean the carburetor. If the above gets you an engine a that will at least run on choke, using Seafoam or similar, added to the tank at a couple ounces per gallon may help. Alternately run the engine a bit, then let it sit a bit. Works often if the blockage isn't complete.
Otherwise, it's a matter of disassembling and cleaning the carb...