You have 3 options when starting with a straight handle bolt.
A) bend the handle, (forging blocks are available and not very pricey)
B) cut off the straight handle and weld on an aftermarket one. (several different ones are available)
C) cut off the handle and use a bolt on replacement.
The only trigger I know of that is available with a pull weight that light is the double set made by new england custom guns. Lightest single set style that I know of is the Timney featherweight at 24oz.