Thanks for the further questions, I understand that this is heartbreaking to see happening with him. I'll answer your questions in order.
1. What else oral medication brand names you can recommend for the treatments you brought above ( Elmiron is the injections only or both?).
2. How can we get this medication?
Elmiron is a human formulation of Pentosan. There aren't any formulations that are labeled for use in cats but we can use the human formulation, Elmiron, at a dose of 1/2 of a 50mg capsule twice daily. It is best given on an empty stomach so your veterinarian may need to have it formulated for him by a compounding pharmacy, splitting the human product into 2 capsules for you. In other countries there are injectable formulations available as Pentosan Injectable for use in dogs and horses. A compounding pharmacy may be able to make that as well and it is given by injection. Most owners choose the pill formulation in cats. I'm sorry I'm not sure what happened to my original response but it should have read "injectable Pentosan or the oral human product (Elmiron trade name)". Somehow some words got left out, my apologies. Pentosan is a prescription product so you can only get it from your veterinarian or via them writing a prescription.
As far as glucosamine/chondroitin products my favorites are Cosequin or Dasuquin.
These are available over the counter, no prescription needed, at pet stores, via Amazon.com and through your veterinarian.
3. What would be a Berrimore's fate of if we do not go for surgery.
Is this process will indefinitely progressing and the damaged legs will become bigger and the bone in the hill will keep growing?
I actually don't think surgery is a great idea for most cats. The bony proliferation will continue no matter what we do, we are just trying to slow it down and cushion the joints. Surgery is for those cats that are crippled, unable to get around comfortably at all and there is no other option. Recovery after surgery is painful, any bone/joint surgery is, and complications like bone or joint infections are possible. I don't think the possible positive benefits nor the comfortable quality of life gained is enough to offset painful surgery in most cases.
I think because this has been a slowly progressive process for him he doesn't realize what normal feels like and is coping with the pain, but I do believe that he does have some pain. As long as he is able to cope and seems happy I think he can go on. Quality of life is so important so watch for changes in personality (hiding when he is usually a social fellow or becoming clingy when he is usually aloof) as that tells us a lot. Watch for changes in appetite too or him unable to enjoy playing.
When we can no longer keep him happy (with the glucosamine/chondroitins, Pentosan and Metacam) then we need to consider humane euthanasia. I cannot say how long that will be because it depends upon how severely he is affected, and how quickly he is progressing. All I can say is if you watch him closely you will know when his quality of life is no longer as good as it should be.
Fortunately I have not had any of these cases personally, but I went to a seminar that discussed them and as soon as I saw your question his symptoms stood out.
Best of luck with your fellow, please let me know if you have any further questions.