I have 5/6 parts now. It seems Pleasure speeder parts are rare and always are special treasure and bound.
If you plan to start search for parts dont do it on a char that finished Dread seed questline, i suppose you will get no armor and higher chance (maybe, not sure) of Pleasure speeder parts as special treasure. I am already overpacked with Dread seed armor pieaces
I thought you couldn't get any of the special items (armor, speeder pieces, etc) if you didn't finish the questline.
Also, just out of curiosity, how many special treasures have you dug up? I am currently 80/100 on X Marks The Spot and I have only found one Pleasure Speeder piece.