Do you have a photo of the parts in question, may be of help to identify, not all on here will have the part numbers etc but may have the parts laying in box of assorted bits and pieces.
A bolt shouldn't be too hard to get, and depending on what the belt retainer looks like it could probably just be made from scratch, parts for the old victa ride ons are damn near impossible now
Not an easy bolt to find, easy if you have a lathe. Only thing I can suggest is a bolt and hunt around for a washer to substitute for the shoulder. Another alternative is to fit a bigger bolt the diameter of the shoulder and use a nyloc nut on it. I would happily make you one but it is the $8.50 postage that kills it.
Ok all good, now the adjuster, very simple job with a welder. Another alternative is to bet a piece of flat bar, bend it at right angle, then open the jaws on a vice and sit the end that needs curving on top of the jaws and with a piece of rod sitting on top, hit it with a hammer and you will get it to curve, not super critical how much curve is needed, just enough so the belt can move over it smoothly
