Insulated pants or zip on bottom insulation? I've a set of EMS insulated pant liners with full length zippers, size Medium. They're Polorfleece with wear panels for the bottom and knees. They were sold as an accessory for EMS snow pants a few years back.
They need a new zipper pull piece on the upper end of the left size, but are in fantastic shape otherwise. On the rare occasions I wear them, I'm just careful not to put much pressure on that end, use the reinforcing Velcro strap, and the zipper holds.
Let me know if you're interested,