First, I'm moving this to the Gun Builders Bench as it really deals with repair rather than shooting your pistol.
I hate to be the bearer of bad tidings but unless you find another pistol like yours or make your own new spring your out of luck.
The pistol was sold by Dixie back in the 1980s but Hoppe's stopped building them after that.
You can not use just any steel to make your spring, it must be a high carbon steel spring stock.
The original spring is .075 thick but this thickness doesn't seem to be available from the suppliers we gun builders commonly use.
Dixie gunworks has some 1/16 (.062) inch spring stock that would work. This 1/16 thick stock won't have quite as much power as the original spring did. They also have some 3/32 (.093) stock that would give greater power than the original spring but that would produce a much higher load on the sear which could damage it.
Here is a link to Dixies material. While your there, I would suggest that you buy one of each thickness.
DIXIE SPRING STOCK
The material is 1 inch wide X 12 inches long which should be enough to make several springs out of sense the finished spring will be about 4 1/2 inches long X 1/4 inch wide.
Cutting this material can be done with a hack saw but you may go thru several hack saw blades before your done.
You may also have to anneal the material to bend it but a propane torch and a small box of sand will do the job.
After bending the spring you will have to re-harden it and temper it but we can help you with that task if and when you decide to fix the gun.
zonie
PS, I posted a link describing how to get this gun to fire reliably some time back.
Here is a link to the post
HOPPE'S PISTOL FIX