1)is this some thing that just happens or is it possible that the spring just got caught up?
It''s possible the spring is broken, but unlikely. I once had my Mossberg 500 turkey gun's mag spring hang up on the magazine plug. Once you get it out, bevel the ends of the wooden dowel so the spring can't get caught in it.
2)where is the best place for me to buy a spring for this?
"If you have any questions regarding the return of your firearm, or need any service information, please telephone us at: (800) 363-3555, fax (830) 773-5893, or email email@example.com"
or Brownells, maybe even Midway. But determine if the spring is actually broken first.
3)what is the proper way to remove the magazine tube?
Remove the barrel and put the receiver in a padded
vise. Use a strap wrench (you can get them from the plumbing department of the hardware store or as a jar opener in the kitchen section) and grab the mag tube by the END where it is reinforced. If you use pliers of any kind and grab it in the middle you'll damage the tube.
If it's really stubborn you may need to heat the receiver with a hair dryer.