OK, I have come up with the keywords for the part you need.
"hand retractable (spring) plunger"
I am pretty good at figuring out hardware and suppliers for items since it is part of my professional background in manufacturing.
The website below shows an example of the dimensions you are going to need to take from your existing parts to find a match for them. I have no idea if Bigfoot
was using metric parts or standard inch measurements. If one of you is in the Seattle area we can meet up and I can take those measurements in person. That way we can get the measurements put into the archives and find a reliable source for a suitable replacement part.
Steel or Stainless Steel Pull Ring - Standard Length - Locking Plungers : Northwestern Tools :
In the diagram in the link above you will see mention of available with or without a locking element. The locking element is typically just a bit of nylon material in a hole that protrudes out into the thread area. This locking element would be good to have as it will help prevent the screw body from backing out of the hole and getting lost due to road vibration. But it would still allow you to remove and replace the part if needed at some future date.