many skins that are listed are not in the bench such as wyvern gloves

I checked on this, it was only the Wyvern Gloves missing because I forgot to set the price on them. I wouldn't consider that "many skins" missing but thanks for pointing it out and it will be fixed in the update.

unable to place bionic giga skin on my giga

Is it a vanilla Giga? This may not be compatible with certain modded dinos but I'll check into this today. May need to recook when the dev kit gets the latest updates (supposedly tomorrow).