I just looked at SEPW.com. Your tiller 1690039 is shown there and they indicate that the bearings are available. Not 100% sure what bearings you need, but my experience has been there are several options for buying bearing replacements once you get the p/n translated into the real bearing p/n (from the bearing manufacturers). :goodl:
If those are the flange bearings for the tiller output shaft, you may find them at a farm/fleet kind of store. That's where I found some for my tiller. Or just take them to your local bearing supply house if you have one.