I have some NOS Shimano Deore DX (MT-60) front tandem cranks if you are interested. Brand-new, nice cranks. 110/74 chainring BCDs, 175mm arms, takes a square taper BB. $40 + shipping if you are interested. (See attached photo... mine look just like these.)
Depending on the pedals you are running, if the axles are removable you can swap the axle left/right and just run standard cranks with standard pedal threads. I did this on one of our stokid crank setups when I ran it on the opposite side from what it was intended.
Or, run the pedals the "wrong" way, but just use lots of blue loctite to keep them from unthreading.
The best way to do it (apart from an actual tandem crank) is to drill out the pedal threads and install Helicoil inserts. Most bikes shops can do this, but it can be expensive as the tools and inserts aren't cheap. Once I also had luck running a pedal tap through messed up threads, but it's a challenge to do that as you need to be very careful to keep the tap straight when it goes in. If not, the pedal will thread on crooked. If you have access to cheap (aka free) cranks at the Co-Op, you could try this tap route first. If it doesn't work, try the Helicoils.