That is the old style Delta trim found in many hardware stores.
I don't think you can get the Delta brand parts, just the after market stuff. Chrome, but not brushed nickel.
Danco shower trim for the Delta 600 series
Danco tub/shower rebuild kits include all of the parts needed to restore your faucet. Give your faucet a face lift and replace all the internal parts to restore your faucet to like new condition.
Fits delta single handle shower valve
For delta series 600 with or without diverter
Includes escutcheon, cap assy, sleeve, handle, button, screws
Rough-in valve not included, sold separately
MFG Brand Name : DANCO
MFG Model # : 89398
MFG Part # : 10021843
Model # 10004
Give your shower a new look by installing an updated trim kit. Replacement is easy and only requires a screwdriver. Offering two handle options, you can choose which style works best for your bath. Kit replaces Delta 600 series with and without diverter in brushed nickel (#70 or #212 Ball) and Delta Monitor 14 series (without volume control) with and without diverter in brushed nickel.
Includes faceplate, 2 handle options, screws, adapters and Allen wrench
Metal handle style only works with valves without diverters
Easy to install