You won't find an OEM Case seat but Ingersoll will have good seats at a price. I have purchased good seats from Farm and Fleet in Wisconsin that are a good replacement for about $40. The bolt pattern is close but not exact so it requires elongating a couple of the holes about 1/4". TSC and other farm/OPE dealers will have good seats but they will have different bolt patterns so, unless buying one from Ingersoll, you'll have to drill or modify the holes a bit.
If drilling holes in your tractor keeps you up at night you may want to look at the seats that have adjustable rails. I didnt have to drill any holes, but i did buy the lazyboy of tractor seats. Sorry, i dont have any pics, my computer got some kind of sickness that required my to reinstall windows and i lost all my pics.
If you're looking to keep it looking original, I bought a couple from Central Tractor that were pretty close and I think they were made by Michigan Seat. I did have to redrill a couple holes though. CT is no longer in business, but you could check through TSC, Big Blue, or any of the other farm and ranch type stores.
The closest to OEM that I have seen is the Michigan seat.
Michigan made the OEM for my 224-79 so I took the cushion off of my new Princess Auto universal seat made by Michigan and put it on the pan of my original seat. I can tell the difference and I'm sure others would see it but I didn't have to drill holes. :trink: