I just went through the same thing. In the end, after stripping the bolt with a standard p-handle hex wrench and a pipe for leverage (with another pipe over the opposing crank for counterforce), I was able to get the bolt off with a spiral bolt extractor and an Irwin Hanson adjustable tap socket. I used a 24' breaker bar on the socket side and a 36" ...
From what I see, it's a lost cause. You mentioned that you'd buy another crank, but that they are not available. It may be time to look for used parts. Ebay is a good source, and there are some bicycle shops that may be able to help. I remember finding a nice selection of used parts at a shop in Seattle several years ago. The good thing about crankarms is ...
Use pipe wrench with small pipe to extend leverage. Once pedal comes off proceed to inspect crank arm threads. Try using correct tap and run it through to freshen up threads. Install new pedal. If you can't tap thread , try a Heli Coil kit to match thread size.
Welcome to galvanic corrosion + threading hell. I'm sorry for your loss.
Alll of the above seem solid, but I'd go slightly differently.
Remove Crank Arm and secure into vise/clamped to table
Lock pair of vise grips onto where the original pedal wrench flats were. Slip cheater bar (any strong metal pole) over the vice grip handles for turning it
Attempt to ...
Do you have access to a drill? buy a screw extractor (AKA easy out) bit and drill through the pedal spindle (from the back side).
I am not sure the crank will be usable: it seems to me that the pedal was wrongly installed. I second the suggestion of get a compatible replacement.
I have been in this position before. This is what finally worked for me:
Take off the crank, put it in a big and stable vise. Alternatively, bolt it to something solid.
Drill a hole through the pedal shaft and put a nail/bolt through it to give the wrench extra grip
Use the biggest wrench you can find. A monkey wrench with a long lever is the best choice. ...