Horsefeathers: try turning the spring around (you probably already did that) but otherwise, you may have to use some needle-nosed pliers to help the the spring onto the retainer plug. I just took my Tok apart and the retainer plug didn't want to come off the end of the spring, but it has been off before. You may need to try and install the plug first, then the spring and see if it press fits together.
Insert your barrel and bushing and position the bushing properly. Turn the slide so the barrel is facing the floor and insert the plug so that it sits evenly in the bushing (portrudes slightly from the bushing). Insert the spring guide into the spring and insert the spring on top of the plug, set the spring guide against the barrel link (which may or may not rest perpendicular to the barrel instead of parallel with it), then mount the slide to the frame. The spring should hold the plug in place until you can manually operate the pistol. If the spring, plug and guide set properly you should be able to fire the pistol without damange to anything except the target.
I have seen some of those pistols come off the battlefield without the spring plugs installed, so apparently the quality control of the wartime (Vietnam) pistols may not have been all that great, yet they functioned just as they should.
If you simply cannot install the spring to the plug, or vice versa, even with the help of some needle nosed pliers, get some new plugs; try SAMCO, SARCO or Gun parts Corp and see if they carry any of those plugs for the Tok - I often see parts for the Tok and plugs might be included. I would simply get two or three, find the one that goes onto the spring best and stash the others. I would also get some new springs from Wolffe. HTH. Mikey.