New Crystals for Federal Gauges

I suspect this subject is beat to death, so I apologize. I'm not doing well with google search.

I have this Federal gauge and one other without a crystal. One was domed and the one in the photo was missing. I do know that some domed crystals are flat and dome when installed.



I wouldn't mind replacing the outer face ring [thousandths increments] as well but it's not really needed. The 6 is rubbed a little weak. I know That in the past I have visited this sub-forum and seen suggested places for sending gauges for servicing. In today's throw it away world they may be out of biz. I did find a place with a minimum three dozen order.

Suggestions for where to buy face parts would be appreciated. Or where to send for servicing. The gauge works smooth and is accurate.
Thanks mike

Well I changed my keyword from Gauge to Gage and added Lens to crystal in my search. That gave me what I needed.
I think I mixed the words gage and gauge once before.

I still didn't get many hits for PM forum threads on the subject. The Metrology forum gets deeper into math skills than my level of training. I still find answers here.
Thanks