I wrecked one arm of my 45 loader a few years ago. Caught the left edge of the bucket on a stump that I'd forgotten about. 4th gear, quick stop, bloody lip. Anyhow - I called a local sale trader and told him I needed a left arm for my loader and he found one for me in about a week. $40 for an old loader, cylinders, rough bucket, rotted hoses, picked up at his shop. Used pieces off of it to repair mine. Have you got a trader in your area - he probably knows where there's one laying in a fence row.
As far as non JD loaders - I modified an old Freeman loader to fit my 630. It was set up for an AC WD-45. Cheap loader - used it for years, but just had to have a 45.