Our local store does handle them, but doing a search of their site, you'll not find them under plow bolts, when typing in the description. They're just listed under "bolt".
https://www.tractorsupply.com/tsc/product/bolt-7-16-in-x-1-1-2-in-2-lb?cm_vc=-10005 I reckon you'd have to blame that on whoever enters the data on their site. I'd have to guess they've never heard of a plow bolt, or have the slightest clue what they are used for.
I know several years back at our local store, they had them marked down for clearance. The manager happened to be close, and I questioned him on them. He said they were going to discontinue them, so if I wanted to stock up, now is the time. Within a year, they were back on the shelf, at a lot higher price than I got them at the clearance price. Apparently enough people raised a ruckus, they got them back in stock.
I doubt many of you remember the TSC stores from the 60's. The closest one we had then was 25 miles away, but they had everything imaginable on shelves. Piston/sleeve sets of the more popular brands, bearing sets, water pumps, generators, and other consumables for rebuilding tractor engines. My Uncle would buy tractors at a monthly farm equipment auction in London, OH. Take them home, tear them down, to see what was needed. Call that store to see if they had the piston/sleeve kits in stock. If not, they'd order it, and either ship, or have it waiting for him on the next trip. Some he would use on the dairy farm, others he'd flip for extra money. 5 lb. boxes of cotter pins of different sizes, and other items like that on shelf you used around the farm. Not blister packs of 2-3.
I'd have to guess they've evolved into the store they are today, because of the small family farms of that era disappearing, and now serving the small 5 acre suburban properties. It didn't help in our particular state, that the gub'ment invoked a inventory tax. So anything left on shelves after the new business fiscal year, is subject to a tax. More than likely why you see year end clearance sales on many items.
I don't know if they still have them, but several years back, they had hard copy master catalogs, that still listed items such as engine kits for tractors, but had to be ordered out of a central warehouse somewhere. 2 years ago, I ordered a 50# bag of sulfur to spread on the potato patch, for $20, the least expensive place I could find around here. Had to order it, but was here in 3 days. I was supposed to pick it up at the local store, but to my surprise Fed Ex delivered it to my door, for that price. Went to order another bag last Spring, only to find they don't carry it anymore. Quite a disappointment, but thank goodness for a small local feed mill/fertilizer dealer handles it. I buy my bulk fertilizer there for the hay field and pasture, and Barry is kind enough to let me get 5 gal. buckets of Sulfur, N, and K for the garden, at bulk price, when they aren't loading out of the bins. Not many places around like that anymore...