Mitred wood for window frame

[obyapka]

Hello, is there anywhere I can buy wood that has already been mitred to build a window frame? Or a frame pre-built to size?
My garage has a wooden window frame, 123cmx107cm and the top opening window has rotted. The sill is also rotted in a small area but this is filled in.
I presume it's best to replace the entire window. As its a garage (and not my house), I should be able to fit it myself, providing I can find the wood, or frame.

Advice appreciated

Thanks in advance.

regards
Brian
in Lancashire

 

[gregers]

very doubtful,the chances of finding timber off the shelf to your exact measurements are unlike me.........SLIM

 

[big-all]

as an aside
you don't buy mitered wood you buy wood and miter it
quality windows and doors are morticed and tenoned often with wedges
but as said there are many sizes sold by many companies but the chances off an off the shelve replacement fitting without alteration will be close to nill