Bret, The taillight panel is held on with wide head sheet metal screws similar to interior screws. You can find them at most auto part stores, they have black oxide finish and stainless. Use the stainless. The screws are made by "Balkamp" and I found them in the local Napa Auto Parts store with part #s:
665-1929 for the Stainless Phillips Round Washer Hd. tapping screws
#8x5/8 in.
665-2075 for the Black Oxide Phillips Round Washer Hd. Tapping Screws
#10x3/4 in.
Not sure if these #s are Balkamp or Napa #s. I gave you both screw sizes as original screws I believe were #8, but if the holes are stripped out, or oversize because of rivets, you may have to go to #10s.
Hope this helps. Mike