That looks like a door that Home Depot sells. I think I have the same doors. I don't remember the Brand name. That's a plastic one piece frame, with fake mullions, and transoms, right? One on outside one on inside. I doubt that HD will have the frame in stock. Take a look at doors they have and if it matches they can tell you manufacturer or order one for you. I dunno if you can get just one side or not.
If I remember right the outside frame is glued to door around edges. I took mine off for painting. It comes off easily with a putty knife and a little paint thinner. Be careful as it holds glass in place. Its at least a two person job, somebody's gotta hold the glass in, and weight of glass can be a surprise if you're not ready for it. The glass may try to fall out when you unscrew inside. It would probably be easier and safer to take door down and do work on padded bench.
Its been a while, but I think I laid the door on a bench, unscrewed the inside, don't remember if it was glued, left that frame in place. With lots of hands holding glass and inside frame, turned door over, then removed outside frame. And I think I over did the thinner and broke seal of glass to door so had to re-caulk. There may have been a foam strip around outer edge of glass. Then I ran a thick bead of siliconized acryllic adhesive caulk around edges to seal the frames back.
I don't think you'll be able to replace just the missing pieces. I don't think you'll be able to find a matching profile in wood molding. But you might luck out, and you might luck out in finding frame. During all that taking apart of my doors I lost the plastic screw hole plugs. Went to HD to see how to order some, guy took me to back room where were a few doors with busted glass, took a packet of plugs off one of them. Your local guy may sell you a frame off a busted one they haven't shipped back yet.
Measure twice, cut once.
Look at the nail, not the hammer. Watch the fence, not the blade.
If you hook your thumb over your belt you won't hit it with the hammer or leave it layin on the saw table.