I do not know why you were told silicone implants are not good for pectus excavatum. I have been using custom made silicone implants for pectus excavatum patients for a number of years with good results. You can find examples in the referenced web page. Since no 2 patients have the exact same defect a custom implant is required if an implant is used to fill the indent. A custom made silicone implant is much cheaper than a custom made porex implant. The implant could be placed via an incision in the scar you have from the previous surgery.
I hope you realize that this format of posting questions and receiving answers lacks the face to face direct communication required for you to make an informed decision regarding your surgery.
My response to your question/post does not represent formal medical advice or constitute a doctor patient relationship. You need to consult with i.e. personally see a board certified plastic surgeon in order to receive a formal evaluation and develop a doctor patient relationship.