I am super late to this party, so much so that I doubt anybody that has posted in it is still active, but happened upon this thread whilst at work, and had to get home to search. I know one of these items, and now I have its stats.
The book I'm referencing is Underdark, a Dungeons & Dragons Campaign Accessory, printed in October 2003, so a ways later than a book here anybody in this thread would have read.
Page 75. Tentacle Extension (Illithid): This item is designed for use by illithids, though any tentacled creature may use one. A single tentacle extension appears as a flexible, 5-foot length of iron composed of many thin iron threads. A razor-sharp blade is attached to the end, and a small duct runs through the length of the extension to convey an illithid's natural flesh-dissolving enzymes to the tip.
A tentacle extension grants the tentacled wearer a +2 enhancement bonus on attack and damage rolls made for that tentacle and increases its base damage die by one step. For illithids, this means that a tentacle attack with a tentacle extension deals base damage of 1d6 instead of 1d4 points. a tentacle extension increases its wearer's reach by 5 feet. A creature with multiple tentacles can wear multiple extensions, if desired.
Strong evocation and transmutation; CL 12th; Craft Magic Arms and Armor or Craft Psionic Arms and Armor, tentacled creature; Price 32,000 gp; Weight 2 lb.