Try Grainger.com Their local store told me they could get any bearing ever manufactured. They did find a match for my 1954 Trojan loader wheel bearing. BG
As noted, try the big industrial suppliers: McMaster-Carr, MSC Industrial Supply, Boston Gear. You may have to slightly modify and off-the-shelf shell, but it can be done.
Worst case scenario, you wind up pouring babbit bearings in place. That may be an old-fashioned method, but it works every time if you know what you're doing.
If I'm not mistaken, Robbo is looking for a plain bearing insert not an anti-friction bearing. I suggest Monmouth or Federal-Mogul bearings. If you have the old bearing take it to a GOOD automotive machine shop and they can match it up. It may cross reference over to a Yanmar, Mitsubishi, Kubota, Lai Dong, or Jai Dong, etc.