I not sure that I have undertood your message
Are you asking about where you can find the silicone for moulding?. Here in Spain I have several suppliers, but no near 18000Km. far of my home
Celestron use moulding silicone because after it secure the mirror with the special nut and washer of cork. Your solution with the metalic sleeve bonded to the mirror with silicone is OK; for me is not the best solution (each engineer have a different idea, you know) because I like to have the open door to a step down, and the mirror bonded with the red silicone is fixed forever...