I think you are confusing silicon (an glass like semiconducting element used to make transistors), silicone (soft rubber based on silicon siloxane compounds) and PVC (clear or coloured plastic tube based on polyvinylchloride).
I have never seen anyone using silicone tubing on their filters, in fact silicone tubing in the required diameter for a filter (say 16mm) would have to have a monsterously thick wall to prevent it stretching or collapsing. Silicone tubing is use in air lines, 4/6mm type.
So what you are actually looking for is PVC tubing as used by virtually all the filter manufacturers. So quick search of Ebay under PVC tube reveals what you want. You probably want "thickwall" version 16/22 or 19/25 or 25/31 for filters as less prone to kinking and collapsing. Also available in green and grey and with reinforcing like Zeus has. Reinforced is nice, as it won't kink or collapse, but its bend radius is much larger.
You can slide PVC pipe over glass lily pipes by dipping the pipe end in boiling water to soften it up first, before sliding it over. My LFS uses silicone (not silicon 😀) oil on lily pipe before sliding the pipe on. You get silicone oil from DIY stores for lubricating push fit plumbing fixings.