There are 2 different types of plow bolts. The ones you mentioned (that resemble a flat-headed carraige bolt) are for the shins, moldboard, landslides, and coverboards (if so equipped) A few replacement shares used these bolts. They come in various diameters and legnths. The 2nd type is what will COMMONLY hold the shares in place. They have a slightly "oval" shaped head. I've seen them in 3/8" and 7/16" diameters and a few various legnths. They are called "clipped head bolts". The manufacturer of the replacement shares should have a listing for size of the bolts for your application. (I'm 90% sure the 101 uses 3/8" X 1-1/4" clipped head's) I'm at work now, and will be until late this evening. If you don't get a definitive answer on which size you need, post back, and I'll look up the size/legnth of clipped head bolts you need when I'm home. They're readily available through a number of sources, inc. Valu-Bilt, Agri-Supply, ect.
Most replacement shares available these days are made by one of a few manufacturers. They are all of satisfactory quality, but none will have an "OEM fit". Under normal conditions, you'll get years of service from them. It takes a LOT of acres to wear out a share.