Those "spacers" are called SPOOLS. Once upon a time, they were available at all the parts "mail order" houses. I've been skimming through catalogs from Valu-Bilt, Shoup, Agri-Supply, ect, and to my amazement, they don't list 'em in their catalogs any longer.
If you know of anyone with an old junk disc laying around, they're more or less the same on just about all disc's with 7" blade spacing.
I've got ONE laying in my shop. How many do you need?
By the way, I'm supposed to head over to where next weeks auction is being held sometime tomorrow. Seems I DO know the folks selling the estate items. It should be in good condition, just well used. The grandson of the diseased works for me now. He's given me quite a bit of insight into the equipment to be sold.