The Home Machinist!

Does anyone know if there are variations of this Regent model? The one I have has a parts list with it that shows a firing pin retraction spring, but there is no spring in the gun, nor any room for it, nor is there a spring stop recess in the FP channel. Numerich Arms, i.e. Gun Parts Corp. shows a similar parts list but shows the spring as unavailable. Of course a lot of other parts are unavailable also, so I don't know if they don't have any or whether there never was one.
There is an hour long Utube video of someone putting one of these together and he claims to install a spring, but the video is extremely unclear on details.
Any help would be appreciated.
--earlgo